Add nullability annotations to core/spring-boot

See gh-46587

config/checkstyle/checkstyle-suppressions.xml

@@ -86,4 +86,8 @@
 	<suppress files="ConfigurationPropertyCaching\.java" checks="SpringJavadoc" message="\@since"/>
 	<suppress files="StructuredLoggingJsonMembersCustomizer\.java" checks="SpringJavadoc" message="\@since"/>
 	<suppress files="FieldValues\.java" checks="SimplifyBooleanExpression" />
+	<!-- jspecify: https://github.com/spring-io/spring-javaformat/issues/454 -->
+	<suppress files="PemPrivateKeyParser\.java" checks="NoWhitespaceBefore" message="'...' is preceded with whitespace"/>
+	<suppress files="Bindable\.java" checks="NoWhitespaceBefore" message="'...' is preceded with whitespace"/>
+	<suppress files="LambdaSafe\.java" checks="NoWhitespaceBefore" message="'...' is preceded with whitespace"/>
 </suppressions>

core/spring-boot/src/main/java/org/springframework/boot/ApplicationArguments.java

@@ -19,6 +19,8 @@ package org.springframework.boot;
 import java.util.List;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Provides access to the arguments that were used to run a {@link SpringApplication}.
  *
@@ -63,7 +65,7 @@ public interface ApplicationArguments {
 	 * @param name the name of the option
 	 * @return a list of option values for the given name
 	 */
-	List<String> getOptionValues(String name);
+	@Nullable List<String> getOptionValues(String name);
 
 	/**
 	 * Return the collection of non-option arguments parsed.

core/spring-boot/src/main/java/org/springframework/boot/ApplicationContextFactory.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeanUtils;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.core.env.ConfigurableEnvironment;
@@ -46,11 +48,12 @@ public interface ApplicationContextFactory {
 	 * Return the {@link Environment} type expected to be set on the
 	 * {@link #create(WebApplicationType) created} application context. The result of this
 	 * method can be used to convert an existing environment instance to the correct type.
-	 * @param webApplicationType the web application type
+	 * @param webApplicationType the web application type or {@code null}
 	 * @return the expected application context type or {@code null} to use the default
 	 * @since 2.6.14
 	 */
-	default Class<? extends ConfigurableEnvironment> getEnvironmentType(WebApplicationType webApplicationType) {
+	default @Nullable Class<? extends ConfigurableEnvironment> getEnvironmentType(
+			@Nullable WebApplicationType webApplicationType) {
 		return null;
 	}
 
@@ -59,11 +62,11 @@ public interface ApplicationContextFactory {
 	 * {@link #create(WebApplicationType) created} application context. The result of this
 	 * method must match the type returned by
 	 * {@link #getEnvironmentType(WebApplicationType)}.
-	 * @param webApplicationType the web application type
+	 * @param webApplicationType the web application type or {@code null}
 	 * @return an environment instance or {@code null} to use the default
 	 * @since 2.6.14
 	 */
-	default ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
+	default @Nullable ConfigurableEnvironment createEnvironment(@Nullable WebApplicationType webApplicationType) {
 		return null;
 	}
 
@@ -73,7 +76,7 @@ public interface ApplicationContextFactory {
 	 * @param webApplicationType the web application type
 	 * @return the newly created application context
 	 */
-	ConfigurableApplicationContext create(WebApplicationType webApplicationType);
+	ConfigurableApplicationContext create(@Nullable WebApplicationType webApplicationType);
 
 	/**
 	 * Creates an {@code ApplicationContextFactory} that will create contexts by

core/spring-boot/src/main/java/org/springframework/boot/ApplicationEnvironment.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.source.ConfigurationPropertySources;
 import org.springframework.core.env.ConfigurablePropertyResolver;
 import org.springframework.core.env.MutablePropertySources;
@@ -29,12 +31,12 @@ import org.springframework.core.env.StandardEnvironment;
 class ApplicationEnvironment extends StandardEnvironment {
 
 	@Override
-	protected String doGetActiveProfilesProperty() {
+	protected @Nullable String doGetActiveProfilesProperty() {
 		return null;
 	}
 
 	@Override
-	protected String doGetDefaultProfilesProperty() {
+	protected @Nullable String doGetDefaultProfilesProperty() {
 		return null;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/ApplicationInfoPropertySource.java

@@ -19,6 +19,8 @@ package org.springframework.boot;
 import java.util.HashMap;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.origin.Origin;
 import org.springframework.boot.origin.OriginLookup;
 import org.springframework.boot.system.ApplicationPid;
@@ -38,7 +40,7 @@ class ApplicationInfoPropertySource extends MapPropertySource implements OriginL
 
 	static final String NAME = "applicationInfo";
 
-	ApplicationInfoPropertySource(Class<?> mainClass) {
+	ApplicationInfoPropertySource(@Nullable Class<?> mainClass) {
 		super(NAME, getProperties(readVersion(mainClass)));
 	}
 
@@ -47,7 +49,7 @@ class ApplicationInfoPropertySource extends MapPropertySource implements OriginL
 	}
 
 	@Override
-	public Origin getOrigin(String key) {
+	public @Nullable Origin getOrigin(String key) {
 		return null;
 	}
 
@@ -56,7 +58,7 @@ class ApplicationInfoPropertySource extends MapPropertySource implements OriginL
 		return true;
 	}
 
-	private static Map<String, Object> getProperties(String applicationVersion) {
+	private static Map<String, Object> getProperties(@Nullable String applicationVersion) {
 		Map<String, Object> result = new HashMap<>();
 		if (StringUtils.hasText(applicationVersion)) {
 			result.put("spring.application.version", applicationVersion);
@@ -68,7 +70,7 @@ class ApplicationInfoPropertySource extends MapPropertySource implements OriginL
 		return result;
 	}
 
-	private static String readVersion(Class<?> applicationClass) {
+	private static @Nullable String readVersion(@Nullable Class<?> applicationClass) {
 		Package sourcePackage = (applicationClass != null) ? applicationClass.getPackage() : null;
 		return (sourcePackage != null) ? sourcePackage.getImplementationVersion() : null;
 	}

core/spring-boot/src/main/java/org/springframework/boot/ApplicationProperties.java

@@ -19,12 +19,15 @@ package org.springframework.boot;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.boot.Banner.Mode;
 import org.springframework.boot.context.properties.bind.BindableRuntimeHintsRegistrar;
 import org.springframework.boot.logging.LoggingSystemProperty;
 import org.springframework.core.env.Environment;
+import org.springframework.util.Assert;
 
 /**
  * Spring application properties.
@@ -48,7 +51,7 @@ class ApplicationProperties {
 	/**
 	 * Mode used to display the banner when the application runs.
 	 */
-	private Banner.Mode bannerMode;
+	private Banner.@Nullable Mode bannerMode;
 
 	/**
 	 * Whether to keep the application alive even if there are no more non-daemon threads.
@@ -80,7 +83,7 @@ class ApplicationProperties {
 	 * Flag to explicitly request a specific type of web application. If not set,
 	 * auto-detected based on the classpath.
 	 */
-	private WebApplicationType webApplicationType;
+	private @Nullable WebApplicationType webApplicationType;
 
 	boolean isAllowBeanDefinitionOverriding() {
 		return this.allowBeanDefinitionOverriding;
@@ -102,12 +105,13 @@ class ApplicationProperties {
 		if (this.bannerMode != null) {
 			return this.bannerMode;
 		}
-		boolean structuredLoggingEnabled = environment
-			.containsProperty(LoggingSystemProperty.CONSOLE_STRUCTURED_FORMAT.getApplicationPropertyName());
+		String applicationPropertyName = LoggingSystemProperty.CONSOLE_STRUCTURED_FORMAT.getApplicationPropertyName();
+		Assert.state(applicationPropertyName != null, "applicationPropertyName must not be null");
+		boolean structuredLoggingEnabled = environment.containsProperty(applicationPropertyName);
 		return (structuredLoggingEnabled) ? Mode.OFF : Banner.Mode.CONSOLE;
 	}
 
-	void setBannerMode(Mode bannerMode) {
+	void setBannerMode(@Nullable Mode bannerMode) {
 		this.bannerMode = bannerMode;
 	}
 
@@ -151,18 +155,18 @@ class ApplicationProperties {
 		this.sources = new LinkedHashSet<>(sources);
 	}
 
-	WebApplicationType getWebApplicationType() {
+	@Nullable WebApplicationType getWebApplicationType() {
 		return this.webApplicationType;
 	}
 
-	void setWebApplicationType(WebApplicationType webApplicationType) {
+	void setWebApplicationType(@Nullable WebApplicationType webApplicationType) {
 		this.webApplicationType = webApplicationType;
 	}
 
 	static class ApplicationPropertiesRuntimeHints implements RuntimeHintsRegistrar {
 
 		@Override
-		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 			BindableRuntimeHintsRegistrar.forTypes(ApplicationProperties.class).registerHints(hints, classLoader);
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/Banner.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.io.PrintStream;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.env.Environment;
 
 /**
@@ -34,10 +36,10 @@ public interface Banner {
 	/**
 	 * Print the banner to the specified print stream.
 	 * @param environment the spring environment
-	 * @param sourceClass the source class for the application
+	 * @param sourceClass the source class for the application or {@code null}
 	 * @param out the output print stream
 	 */
-	void printBanner(Environment environment, Class<?> sourceClass, PrintStream out);
+	void printBanner(Environment environment, @Nullable Class<?> sourceClass, PrintStream out);
 
 	/**
 	 * An enumeration of possible values for configuring the Banner.

core/spring-boot/src/main/java/org/springframework/boot/BeanDefinitionLoader.java

@@ -23,6 +23,7 @@ import java.util.Set;
 import java.util.regex.Pattern;
 
 import groovy.lang.Closure;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.BeanDefinitionStoreException;
@@ -68,11 +69,11 @@ class BeanDefinitionLoader {
 
 	private final AbstractBeanDefinitionReader xmlReader;
 
-	private final BeanDefinitionReader groovyReader;
+	private final @Nullable BeanDefinitionReader groovyReader;
 
 	private final ClassPathBeanDefinitionScanner scanner;
 
-	private ResourceLoader resourceLoader;
+	private @Nullable ResourceLoader resourceLoader;
 
 	/**
 	 * Create a new {@link BeanDefinitionLoader} that will load beans into the specified
@@ -86,7 +87,7 @@ class BeanDefinitionLoader {
 		this.sources = sources;
 		this.annotatedReader = new AnnotatedBeanDefinitionReader(registry);
 		this.xmlReader = new XmlBeanDefinitionReader(registry);
-		this.groovyReader = (isGroovyPresent() ? new GroovyBeanDefinitionReader(registry) : null);
+		this.groovyReader = isGroovyPresent() ? new GroovyBeanDefinitionReader(registry) : null;
 		this.scanner = new ClassPathBeanDefinitionScanner(registry);
 		this.scanner.addExcludeFilter(new ClassExcludeFilter(sources));
 	}
@@ -152,7 +153,7 @@ class BeanDefinitionLoader {
 	}
 
 	private void load(Class<?> source) {
-		if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
+		if (this.groovyReader != null && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
 			// Any GroovyLoaders added in beans{} DSL can contribute beans here
 			GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
 			((GroovyBeanDefinitionReader) this.groovyReader).beans(loader.getBeans());
@@ -163,7 +164,9 @@ class BeanDefinitionLoader {
 	}
 
 	private void load(Resource source) {
-		if (source.getFilename().endsWith(".groovy")) {
+		String filename = source.getFilename();
+		Assert.state(filename != null, "Source has no filename");
+		if (filename.endsWith(".groovy")) {
 			if (this.groovyReader == null) {
 				throw new BeanDefinitionStoreException("Cannot load Groovy beans without Groovy on classpath");
 			}
@@ -231,7 +234,7 @@ class BeanDefinitionLoader {
 		}
 	}
 
-	private boolean isLoadCandidate(Resource resource) {
+	private boolean isLoadCandidate(@Nullable Resource resource) {
 		if (resource == null || !resource.exists()) {
 			return false;
 		}
@@ -253,7 +256,7 @@ class BeanDefinitionLoader {
 		return true;
 	}
 
-	private Package findPackage(CharSequence source) {
+	private @Nullable Package findPackage(CharSequence source) {
 		Package pkg = getClass().getClassLoader().getDefinedPackage(source.toString());
 		if (pkg != null) {
 			return pkg;
@@ -264,7 +267,9 @@ class BeanDefinitionLoader {
 			Resource[] resources = resolver
 				.getResources(ClassUtils.convertClassNameToResourcePath(source.toString()) + "/*.class");
 			for (Resource resource : resources) {
-				String className = StringUtils.stripFilenameExtension(resource.getFilename());
+				String filename = resource.getFilename();
+				Assert.state(filename != null, "No filename available");
+				String className = StringUtils.stripFilenameExtension(filename);
 				load(Class.forName(source + "." + className));
 				break;
 			}

core/spring-boot/src/main/java/org/springframework/boot/BootstrapContext.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationContext;
 import org.springframework.core.env.Environment;
 
@@ -41,7 +43,7 @@ public interface BootstrapContext {
 	 * @return the instance managed by the context
 	 * @throws IllegalStateException if the type has not been registered
 	 */
-	<T> T get(Class<T> type) throws IllegalStateException;
+	<T> @Nullable T get(Class<T> type) throws IllegalStateException;
 
 	/**
 	 * Return an instance from the context if the type has been registered. The instance
@@ -51,7 +53,7 @@ public interface BootstrapContext {
 	 * @param other the instance to use if the type has not been registered
 	 * @return the instance
 	 */
-	<T> T getOrElse(Class<T> type, T other);
+	<T> @Nullable T getOrElse(Class<T> type, @Nullable T other);
 
 	/**
 	 * Return an instance from the context if the type has been registered. The instance
@@ -61,7 +63,7 @@ public interface BootstrapContext {
 	 * @param other a supplier for the instance to use if the type has not been registered
 	 * @return the instance
 	 */
-	<T> T getOrElseSupply(Class<T> type, Supplier<T> other);
+	<T> @Nullable T getOrElseSupply(Class<T> type, Supplier<@Nullable T> other);
 
 	/**
 	 * Return an instance from the context if the type has been registered. The instance
@@ -74,7 +76,8 @@ public interface BootstrapContext {
 	 * @throws X if the type has not been registered
 	 * @throws IllegalStateException if the type has not been registered
 	 */
-	<T, X extends Throwable> T getOrElseThrow(Class<T> type, Supplier<? extends X> exceptionSupplier) throws X;
+	<T, X extends Throwable> @Nullable T getOrElseThrow(Class<T> type, Supplier<? extends X> exceptionSupplier)
+			throws X;
 
 	/**
 	 * Return if a registration exists for the given type.

core/spring-boot/src/main/java/org/springframework/boot/BootstrapRegistry.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.env.Environment;
@@ -78,7 +80,7 @@ public interface BootstrapRegistry {
 	 * @param type the instance type
 	 * @return the registered {@link InstanceSupplier} or {@code null}
 	 */
-	<T> InstanceSupplier<T> getRegisteredInstanceSupplier(Class<T> type);
+	<T> @Nullable InstanceSupplier<T> getRegisteredInstanceSupplier(Class<T> type);
 
 	/**
 	 * Add an {@link ApplicationListener} that will be called with a
@@ -101,9 +103,9 @@ public interface BootstrapRegistry {
 		 * Factory method used to create the instance when needed.
 		 * @param context the {@link BootstrapContext} which may be used to obtain other
 		 * bootstrap instances.
-		 * @return the instance
+		 * @return the instance or {@code null}
 		 */
-		T get(BootstrapContext context);
+		@Nullable T get(BootstrapContext context);
 
 		/**
 		 * Return the scope of the supplied instance.
@@ -126,7 +128,7 @@ public interface BootstrapRegistry {
 			return new InstanceSupplier<>() {
 
 				@Override
-				public T get(BootstrapContext context) {
+				public @Nullable T get(BootstrapContext context) {
 					return parent.get(context);
 				}
 
@@ -145,7 +147,7 @@ public interface BootstrapRegistry {
 		 * @param instance the instance
 		 * @return a new {@link InstanceSupplier}
 		 */
-		static <T> InstanceSupplier<T> of(T instance) {
+		static <T> InstanceSupplier<T> of(@Nullable T instance) {
 			return (registry) -> instance;
 		}
 
@@ -156,7 +158,7 @@ public interface BootstrapRegistry {
 		 * @param supplier the supplier that will provide the instance
 		 * @return a new {@link InstanceSupplier}
 		 */
-		static <T> InstanceSupplier<T> from(Supplier<T> supplier) {
+		static <T> InstanceSupplier<T> from(@Nullable Supplier<T> supplier) {
 			return (registry) -> (supplier != null) ? supplier.get() : null;
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/ClearCachesApplicationListener.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.lang.reflect.Method;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.event.ContextRefreshedEvent;
 import org.springframework.util.ReflectionUtils;
@@ -35,7 +37,7 @@ class ClearCachesApplicationListener implements ApplicationListener<ContextRefre
 		clearClassLoaderCaches(Thread.currentThread().getContextClassLoader());
 	}
 
-	private void clearClassLoaderCaches(ClassLoader classLoader) {
+	private void clearClassLoaderCaches(@Nullable ClassLoader classLoader) {
 		if (classLoader == null) {
 			return;
 		}

core/spring-boot/src/main/java/org/springframework/boot/DefaultApplicationArguments.java

@@ -22,6 +22,8 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.env.SimpleCommandLinePropertySource;
 import org.springframework.util.Assert;
 
@@ -60,7 +62,7 @@ public class DefaultApplicationArguments implements ApplicationArguments {
 	}
 
 	@Override
-	public List<String> getOptionValues(String name) {
+	public @Nullable List<String> getOptionValues(String name) {
 		List<String> values = this.source.getOptionValues(name);
 		return (values != null) ? Collections.unmodifiableList(values) : null;
 	}
@@ -82,7 +84,7 @@ public class DefaultApplicationArguments implements ApplicationArguments {
 		}
 
 		@Override
-		public List<String> getOptionValues(String name) {
+		public @Nullable List<String> getOptionValues(String name) {
 			return super.getOptionValues(name);
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/DefaultApplicationContextFactory.java

@@ -19,12 +19,15 @@ package org.springframework.boot;
 import java.util.function.BiFunction;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.AotDetector;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.support.GenericApplicationContext;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.io.support.SpringFactoriesLoader;
+import org.springframework.lang.Contract;
 
 /**
  * Default {@link ApplicationContextFactory} implementation that will create an
@@ -34,18 +37,25 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
  */
 class DefaultApplicationContextFactory implements ApplicationContextFactory {
 
+	// Method reference is not detected with correct nullability
+	@SuppressWarnings("NullAway")
 	@Override
-	public Class<? extends ConfigurableEnvironment> getEnvironmentType(WebApplicationType webApplicationType) {
+	public @Nullable Class<? extends ConfigurableEnvironment> getEnvironmentType(
+			@Nullable WebApplicationType webApplicationType) {
 		return getFromSpringFactories(webApplicationType, ApplicationContextFactory::getEnvironmentType, null);
 	}
 
+	// Method reference is not detected with correct nullability
+	@SuppressWarnings("NullAway")
 	@Override
-	public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
+	public @Nullable ConfigurableEnvironment createEnvironment(@Nullable WebApplicationType webApplicationType) {
 		return getFromSpringFactories(webApplicationType, ApplicationContextFactory::createEnvironment, null);
 	}
 
+	// Method reference is not detected with correct nullability
+	@SuppressWarnings("NullAway")
 	@Override
-	public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
+	public ConfigurableApplicationContext create(@Nullable WebApplicationType webApplicationType) {
 		try {
 			return getFromSpringFactories(webApplicationType, ApplicationContextFactory::create,
 					this::createDefaultApplicationContext);
@@ -63,8 +73,10 @@ class DefaultApplicationContextFactory implements ApplicationContextFactory {
 		return new GenericApplicationContext();
 	}
 
-	private <T> T getFromSpringFactories(WebApplicationType webApplicationType,
-			BiFunction<ApplicationContextFactory, WebApplicationType, T> action, Supplier<T> defaultResult) {
+	@Contract("_, _, !null -> !null")
+	private <T> @Nullable T getFromSpringFactories(@Nullable WebApplicationType webApplicationType,
+			BiFunction<ApplicationContextFactory, @Nullable WebApplicationType, @Nullable T> action,
+			@Nullable Supplier<T> defaultResult) {
 		for (ApplicationContextFactory candidate : SpringFactoriesLoader.loadFactories(ApplicationContextFactory.class,
 				getClass().getClassLoader())) {
 			T result = action.apply(candidate, webApplicationType);

core/spring-boot/src/main/java/org/springframework/boot/DefaultBootstrapContext.java

@@ -20,6 +20,8 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.ConfigurableApplicationContext;
@@ -72,7 +74,7 @@ public class DefaultBootstrapContext implements ConfigurableBootstrapContext {
 
 	@Override
 	@SuppressWarnings("unchecked")
-	public <T> InstanceSupplier<T> getRegisteredInstanceSupplier(Class<T> type) {
+	public <T> @Nullable InstanceSupplier<T> getRegisteredInstanceSupplier(Class<T> type) {
 		synchronized (this.instanceSuppliers) {
 			return (InstanceSupplier<T>) this.instanceSuppliers.get(type);
 		}
@@ -84,17 +86,18 @@ public class DefaultBootstrapContext implements ConfigurableBootstrapContext {
 	}
 
 	@Override
-	public <T> T get(Class<T> type) throws IllegalStateException {
+	public <T> @Nullable T get(Class<T> type) throws IllegalStateException {
 		return getOrElseThrow(type, () -> new IllegalStateException(type.getName() + " has not been registered"));
 	}
 
 	@Override
-	public <T> T getOrElse(Class<T> type, T other) {
+	@SuppressWarnings("NullAway") // Doesn't detect lambda with correct nullability
+	public <T> @Nullable T getOrElse(Class<T> type, @Nullable T other) {
 		return getOrElseSupply(type, () -> other);
 	}
 
 	@Override
-	public <T> T getOrElseSupply(Class<T> type, Supplier<T> other) {
+	public <T> @Nullable T getOrElseSupply(Class<T> type, Supplier<@Nullable T> other) {
 		synchronized (this.instanceSuppliers) {
 			InstanceSupplier<?> instanceSupplier = this.instanceSuppliers.get(type);
 			return (instanceSupplier != null) ? getInstance(type, instanceSupplier) : other.get();
@@ -102,7 +105,8 @@ public class DefaultBootstrapContext implements ConfigurableBootstrapContext {
 	}
 
 	@Override
-	public <T, X extends Throwable> T getOrElseThrow(Class<T> type, Supplier<? extends X> exceptionSupplier) throws X {
+	public <T, X extends Throwable> @Nullable T getOrElseThrow(Class<T> type, Supplier<? extends X> exceptionSupplier)
+			throws X {
 		synchronized (this.instanceSuppliers) {
 			InstanceSupplier<?> instanceSupplier = this.instanceSuppliers.get(type);
 			if (instanceSupplier == null) {
@@ -113,10 +117,13 @@ public class DefaultBootstrapContext implements ConfigurableBootstrapContext {
 	}
 
 	@SuppressWarnings("unchecked")
-	private <T> T getInstance(Class<T> type, InstanceSupplier<?> instanceSupplier) {
+	private <T> @Nullable T getInstance(Class<T> type, InstanceSupplier<?> instanceSupplier) {
 		T instance = (T) this.instances.get(type);
 		if (instance == null) {
 			instance = (T) instanceSupplier.get(this);
+			if (instance == null) {
+				return null;
+			}
 			if (instanceSupplier.getScope() == Scope.SINGLETON) {
 				this.instances.put(type, instance);
 			}

core/spring-boot/src/main/java/org/springframework/boot/DefaultPropertiesPropertySource.java

@@ -20,6 +20,8 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Consumer;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;
 import org.springframework.core.env.MapPropertySource;
@@ -56,7 +58,7 @@ public class DefaultPropertiesPropertySource extends MapPropertySource {
 	 * @param propertySource the property source to check
 	 * @return {@code true} if the name matches
 	 */
-	public static boolean hasMatchingName(PropertySource<?> propertySource) {
+	public static boolean hasMatchingName(@Nullable PropertySource<?> propertySource) {
 		return (propertySource != null) && propertySource.getName().equals(NAME);
 	}
 
@@ -67,7 +69,8 @@ public class DefaultPropertiesPropertySource extends MapPropertySource {
 	 * @param action the action used to consume the
 	 * {@link DefaultPropertiesPropertySource}
 	 */
-	public static void ifNotEmpty(Map<String, Object> source, Consumer<DefaultPropertiesPropertySource> action) {
+	public static void ifNotEmpty(Map<String, Object> source,
+			@Nullable Consumer<DefaultPropertiesPropertySource> action) {
 		if (!CollectionUtils.isEmpty(source) && action != null) {
 			action.accept(new DefaultPropertiesPropertySource(source));
 		}

core/spring-boot/src/main/java/org/springframework/boot/LazyInitializationBeanFactoryPostProcessor.java

@@ -19,6 +19,8 @@ package org.springframework.boot;
 import java.util.ArrayList;
 import java.util.Collection;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.SmartInitializingSingleton;
@@ -84,7 +86,7 @@ public final class LazyInitializationBeanFactoryPostProcessor implements BeanFac
 		}
 	}
 
-	private Class<?> getBeanType(ConfigurableListableBeanFactory beanFactory, String beanName) {
+	private @Nullable Class<?> getBeanType(ConfigurableListableBeanFactory beanFactory, String beanName) {
 		try {
 			return beanFactory.getType(beanName, false);
 		}
@@ -94,7 +96,7 @@ public final class LazyInitializationBeanFactoryPostProcessor implements BeanFac
 	}
 
 	private boolean isExcluded(Collection<LazyInitializationExcludeFilter> filters, String beanName,
-			AbstractBeanDefinition beanDefinition, Class<?> beanType) {
+			AbstractBeanDefinition beanDefinition, @Nullable Class<?> beanType) {
 		if (beanType != null) {
 			for (LazyInitializationExcludeFilter filter : filters) {
 				if (filter.isExcluded(beanName, beanDefinition, beanType)) {

core/spring-boot/src/main/java/org/springframework/boot/ResourceBanner.java

@@ -28,6 +28,7 @@ import java.util.Map;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.ansi.AnsiPropertySource;
 import org.springframework.core.env.ConfigurableEnvironment;
@@ -64,7 +65,7 @@ public class ResourceBanner implements Banner {
 	}
 
 	@Override
-	public void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {
+	public void printBanner(Environment environment, @Nullable Class<?> sourceClass, PrintStream out) {
 		try (InputStream input = this.resource.getInputStream()) {
 			String banner = StreamUtils.copyToString(input,
 					environment.getProperty("spring.banner.charset", Charset.class, StandardCharsets.UTF_8));
@@ -86,32 +87,32 @@ public class ResourceBanner implements Banner {
 	 * @param sourceClass the source class
 	 * @return a mutable list of property resolvers
 	 */
-	protected List<PropertyResolver> getPropertyResolvers(Environment environment, Class<?> sourceClass) {
+	protected List<PropertyResolver> getPropertyResolvers(Environment environment, @Nullable Class<?> sourceClass) {
 		List<PropertyResolver> resolvers = new ArrayList<>();
 		resolvers.add(new PropertySourcesPropertyResolver(createNullDefaultSources(environment, sourceClass)));
 		resolvers.add(new PropertySourcesPropertyResolver(createEmptyDefaultSources(environment, sourceClass)));
 		return resolvers;
 	}
 
-	private MutablePropertySources createNullDefaultSources(Environment environment, Class<?> sourceClass) {
+	private MutablePropertySources createNullDefaultSources(Environment environment, @Nullable Class<?> sourceClass) {
 		MutablePropertySources nullDefaultSources = new MutablePropertySources();
 		if (environment instanceof ConfigurableEnvironment configurableEnvironment) {
 			configurableEnvironment.getPropertySources().forEach(nullDefaultSources::addLast);
 		}
 		nullDefaultSources.addLast(getTitleSource(sourceClass, null));
 		nullDefaultSources.addLast(getAnsiSource());
-		nullDefaultSources.addLast(getVersionSource(sourceClass, environment, null));
+		nullDefaultSources.addLast(getVersionSource(environment, null));
 		return nullDefaultSources;
 	}
 
-	private MutablePropertySources createEmptyDefaultSources(Environment environment, Class<?> sourceClass) {
+	private MutablePropertySources createEmptyDefaultSources(Environment environment, @Nullable Class<?> sourceClass) {
 		MutablePropertySources emptyDefaultSources = new MutablePropertySources();
 		emptyDefaultSources.addLast(getTitleSource(sourceClass, ""));
-		emptyDefaultSources.addLast(getVersionSource(sourceClass, environment, ""));
+		emptyDefaultSources.addLast(getVersionSource(environment, ""));
 		return emptyDefaultSources;
 	}
 
-	private MapPropertySource getTitleSource(Class<?> sourceClass, String defaultValue) {
+	private MapPropertySource getTitleSource(@Nullable Class<?> sourceClass, @Nullable String defaultValue) {
 		String applicationTitle = getApplicationTitle(sourceClass);
 		Map<String, Object> titleMap = Collections.singletonMap("application.title",
 				(applicationTitle != null) ? applicationTitle : defaultValue);
@@ -124,7 +125,7 @@ public class ResourceBanner implements Banner {
 	 * @param sourceClass the source class
 	 * @return the application title
 	 */
-	protected String getApplicationTitle(Class<?> sourceClass) {
+	protected @Nullable String getApplicationTitle(@Nullable Class<?> sourceClass) {
 		Package sourcePackage = (sourceClass != null) ? sourceClass.getPackage() : null;
 		return (sourcePackage != null) ? sourcePackage.getImplementationTitle() : null;
 	}
@@ -133,11 +134,11 @@ public class ResourceBanner implements Banner {
 		return new AnsiPropertySource("ansi", true);
 	}
 
-	private MapPropertySource getVersionSource(Class<?> sourceClass, Environment environment, String defaultValue) {
-		return new MapPropertySource("version", getVersionsMap(sourceClass, environment, defaultValue));
+	private MapPropertySource getVersionSource(Environment environment, @Nullable String defaultValue) {
+		return new MapPropertySource("version", getVersionsMap(environment, defaultValue));
 	}
 
-	private Map<String, Object> getVersionsMap(Class<?> sourceClass, Environment environment, String defaultValue) {
+	private Map<String, Object> getVersionsMap(Environment environment, @Nullable String defaultValue) {
 		String appVersion = getApplicationVersion(environment);
 		String bootVersion = getBootVersion();
 		Map<String, Object> versions = new HashMap<>();
@@ -148,7 +149,7 @@ public class ResourceBanner implements Banner {
 		return versions;
 	}
 
-	private String getApplicationVersion(Environment environment) {
+	private @Nullable String getApplicationVersion(Environment environment) {
 		return environment.getProperty("spring.application.version");
 	}
 
@@ -156,7 +157,7 @@ public class ResourceBanner implements Banner {
 		return SpringBootVersion.getVersion();
 	}
 
-	private String getVersionString(String version, boolean format, String fallback) {
+	private @Nullable String getVersionString(@Nullable String version, boolean format, @Nullable String fallback) {
 		if (version == null) {
 			return fallback;
 		}

core/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -41,6 +41,7 @@ import java.util.stream.Stream;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.crac.management.CRaCMXBean;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.aot.AotDetector;
 import org.springframework.beans.BeansException;
@@ -204,27 +205,27 @@ public class SpringApplication {
 
 	private final Set<Class<?>> primarySources;
 
-	private Class<?> mainApplicationClass;
+	private @Nullable Class<?> mainApplicationClass;
 
 	private boolean addCommandLineProperties = true;
 
 	private boolean addConversionService = true;
 
-	private Banner banner;
+	private @Nullable Banner banner;
 
-	private ResourceLoader resourceLoader;
+	private @Nullable ResourceLoader resourceLoader;
 
-	private BeanNameGenerator beanNameGenerator;
+	private @Nullable BeanNameGenerator beanNameGenerator;
 
-	private ConfigurableEnvironment environment;
+	private @Nullable ConfigurableEnvironment environment;
 
 	private boolean headless = true;
 
-	private List<ApplicationContextInitializer<?>> initializers;
+	private List<ApplicationContextInitializer<?>> initializers = new ArrayList<>();
 
-	private List<ApplicationListener<?>> listeners;
+	private List<ApplicationListener<?>> listeners = new ArrayList<>();
 
-	private Map<String, Object> defaultProperties;
+	private @Nullable Map<String, Object> defaultProperties;
 
 	private final List<BootstrapRegistryInitializer> bootstrapRegistryInitializers;
 
@@ -232,7 +233,7 @@ public class SpringApplication {
 
 	private boolean isCustomEnvironment;
 
-	private String environmentPrefix;
+	private @Nullable String environmentPrefix;
 
 	private ApplicationContextFactory applicationContextFactory = ApplicationContextFactory.DEFAULT;
 
@@ -265,7 +266,7 @@ public class SpringApplication {
 	 * @see #setSources(Set)
 	 */
 	@SuppressWarnings({ "unchecked", "rawtypes" })
-	public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
+	public SpringApplication(@Nullable ResourceLoader resourceLoader, Class<?>... primarySources) {
 		this.resourceLoader = resourceLoader;
 		Assert.notNull(primarySources, "'primarySources' must not be null");
 		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
@@ -277,7 +278,7 @@ public class SpringApplication {
 		this.mainApplicationClass = deduceMainApplicationClass();
 	}
 
-	private Class<?> deduceMainApplicationClass() {
+	private @Nullable Class<?> deduceMainApplicationClass() {
 		return StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE)
 			.walk(this::findMainClass)
 			.orElse(null);
@@ -314,11 +315,11 @@ public class SpringApplication {
 			prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
 			refreshContext(context);
 			afterRefresh(context, applicationArguments);
-			startup.started();
+			Duration timeTakenToStarted = startup.started();
 			if (this.properties.isLogStartupInfo()) {
 				new StartupInfoLogger(this.mainApplicationClass, environment).logStarted(getApplicationLog(), startup);
 			}
-			listeners.started(context, startup.timeTakenToStarted());
+			listeners.started(context, timeTakenToStarted);
 			callRunners(context, applicationArguments);
 		}
 		catch (Throwable ex) {
@@ -373,7 +374,7 @@ public class SpringApplication {
 
 	private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
 			ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
-			ApplicationArguments applicationArguments, Banner printedBanner) {
+			ApplicationArguments applicationArguments, @Nullable Banner printedBanner) {
 		context.setEnvironment(environment);
 		postProcessApplicationContext(context);
 		addAotGeneratedInitializerIfNecessary(this.initializers);
@@ -417,6 +418,7 @@ public class SpringApplication {
 			List<ApplicationContextInitializer<?>> aotInitializers = new ArrayList<>(
 					initializers.stream().filter(AotApplicationContextInitializer.class::isInstance).toList());
 			if (aotInitializers.isEmpty()) {
+				Assert.state(this.mainApplicationClass != null, "No application main class found");
 				String initializerClassName = this.mainApplicationClass.getName() + "__ApplicationContextInitializer";
 				if (!ClassUtils.isPresent(initializerClassName, getClassLoader())) {
 					throw new AotInitializerNotFoundException(this.mainApplicationClass, initializerClassName);
@@ -458,7 +460,7 @@ public class SpringApplication {
 		return getSpringFactoriesInstances(type, null);
 	}
 
-	private <T> List<T> getSpringFactoriesInstances(Class<T> type, ArgumentResolver argumentResolver) {
+	private <T> List<T> getSpringFactoriesInstances(Class<T> type, @Nullable ArgumentResolver argumentResolver) {
 		return SpringFactoriesLoader.forDefaultResourceLocation(getClassLoader()).load(type, argumentResolver);
 	}
 
@@ -507,8 +509,8 @@ public class SpringApplication {
 		}
 		if (this.addCommandLineProperties && args.length > 0) {
 			String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
-			if (sources.contains(name)) {
-				PropertySource<?> source = sources.get(name);
+			PropertySource<?> source = sources.get(name);
+			if (source != null) {
 				CompositePropertySource composite = new CompositePropertySource(name);
 				composite
 					.addPropertySource(new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
@@ -546,7 +548,7 @@ public class SpringApplication {
 		}
 	}
 
-	private Banner printBanner(ConfigurableEnvironment environment) {
+	private @Nullable Banner printBanner(ConfigurableEnvironment environment) {
 		if (this.properties.getBannerMode(environment) == Banner.Mode.OFF) {
 			return null;
 		}
@@ -604,6 +606,8 @@ public class SpringApplication {
 		for (ApplicationContextInitializer initializer : getInitializers()) {
 			Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),
 					ApplicationContextInitializer.class);
+			Assert.state(requiredType != null,
+					() -> "No generic type found for initializr of type " + initializer.getClass());
 			Assert.state(requiredType.isInstance(context), "Unable to call initializer");
 			initializer.initialize(context);
 		}
@@ -685,9 +689,9 @@ public class SpringApplication {
 	/**
 	 * The ResourceLoader that will be used in the ApplicationContext.
 	 * @return the resourceLoader the resource loader that will be used in the
-	 * ApplicationContext (or null if the default)
+	 * ApplicationContext (or {@code null} if the default)
 	 */
-	public ResourceLoader getResourceLoader() {
+	public @Nullable ResourceLoader getResourceLoader() {
 		return this.resourceLoader;
 	}
 
@@ -699,9 +703,13 @@ public class SpringApplication {
 	 */
 	public ClassLoader getClassLoader() {
 		if (this.resourceLoader != null) {
-			return this.resourceLoader.getClassLoader();
+			ClassLoader classLoader = this.resourceLoader.getClassLoader();
+			Assert.state(classLoader != null, "No classloader found");
+			return classLoader;
 		}
-		return ClassUtils.getDefaultClassLoader();
+		ClassLoader classLoader = ClassUtils.getDefaultClassLoader();
+		Assert.state(classLoader != null, "No classloader found");
+		return classLoader;
 	}
 
 	/**
@@ -781,8 +789,8 @@ public class SpringApplication {
 			.accept((R) runner);
 	}
 
-	private RuntimeException handleRunFailure(ConfigurableApplicationContext context, Throwable exception,
-			SpringApplicationRunListeners listeners) {
+	private RuntimeException handleRunFailure(@Nullable ConfigurableApplicationContext context, Throwable exception,
+			@Nullable SpringApplicationRunListeners listeners) {
 		if (exception instanceof AbandonedRunException abandonedRunException) {
 			return abandonedRunException;
 		}
@@ -808,9 +816,11 @@ public class SpringApplication {
 				: new IllegalStateException(exception);
 	}
 
-	private Collection<SpringBootExceptionReporter> getExceptionReporters(ConfigurableApplicationContext context) {
+	private Collection<SpringBootExceptionReporter> getExceptionReporters(
+			@Nullable ConfigurableApplicationContext context) {
 		try {
-			ArgumentResolver argumentResolver = ArgumentResolver.of(ConfigurableApplicationContext.class, context);
+			ArgumentResolver argumentResolver = (context != null)
+					? ArgumentResolver.of(ConfigurableApplicationContext.class, context) : ArgumentResolver.none();
 			return getSpringFactoriesInstances(SpringBootExceptionReporter.class, argumentResolver);
 		}
 		catch (Throwable ex) {
@@ -857,7 +867,7 @@ public class SpringApplication {
 		}
 	}
 
-	private void handleExitCode(ConfigurableApplicationContext context, Throwable exception) {
+	private void handleExitCode(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		int exitCode = getExitCodeFromException(context, exception);
 		if (exitCode != 0) {
 			if (context != null) {
@@ -870,7 +880,7 @@ public class SpringApplication {
 		}
 	}
 
-	private int getExitCodeFromException(ConfigurableApplicationContext context, Throwable exception) {
+	private int getExitCodeFromException(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		int exitCode = getExitCodeFromMappedException(context, exception);
 		if (exitCode == 0) {
 			exitCode = getExitCodeFromExitCodeGeneratorException(exception);
@@ -878,7 +888,7 @@ public class SpringApplication {
 		return exitCode;
 	}
 
-	private int getExitCodeFromMappedException(ConfigurableApplicationContext context, Throwable exception) {
+	private int getExitCodeFromMappedException(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		if (context == null || !context.isActive()) {
 			return 0;
 		}
@@ -888,7 +898,7 @@ public class SpringApplication {
 		return generators.getExitCode();
 	}
 
-	private int getExitCodeFromExitCodeGeneratorException(Throwable exception) {
+	private int getExitCodeFromExitCodeGeneratorException(@Nullable Throwable exception) {
 		if (exception == null) {
 			return 0;
 		}
@@ -898,7 +908,7 @@ public class SpringApplication {
 		return getExitCodeFromExitCodeGeneratorException(exception.getCause());
 	}
 
-	SpringBootExceptionHandler getSpringBootExceptionHandler() {
+	@Nullable SpringBootExceptionHandler getSpringBootExceptionHandler() {
 		if (isMainThread(Thread.currentThread())) {
 			return SpringBootExceptionHandler.forCurrentThread();
 		}
@@ -914,7 +924,7 @@ public class SpringApplication {
 	 * Returns the main application class that has been deduced or explicitly configured.
 	 * @return the main application class or {@code null}
 	 */
-	public Class<?> getMainApplicationClass() {
+	public @Nullable Class<?> getMainApplicationClass() {
 		return this.mainApplicationClass;
 	}
 
@@ -924,7 +934,7 @@ public class SpringApplication {
 	 * Can be set to {@code null} if there is no explicit application class.
 	 * @param mainApplicationClass the mainApplicationClass to set or {@code null}
 	 */
-	public void setMainApplicationClass(Class<?> mainApplicationClass) {
+	public void setMainApplicationClass(@Nullable Class<?> mainApplicationClass) {
 		this.mainApplicationClass = mainApplicationClass;
 	}
 
@@ -933,7 +943,7 @@ public class SpringApplication {
 	 * @return the type of web application
 	 * @since 2.0.0
 	 */
-	public WebApplicationType getWebApplicationType() {
+	public @Nullable WebApplicationType getWebApplicationType() {
 		return this.properties.getWebApplicationType();
 	}
 
@@ -1107,7 +1117,7 @@ public class SpringApplication {
 	 * context.
 	 * @param environment the environment
 	 */
-	public void setEnvironment(ConfigurableEnvironment environment) {
+	public void setEnvironment(@Nullable ConfigurableEnvironment environment) {
 		this.isCustomEnvironment = true;
 		this.environment = environment;
 	}
@@ -1191,7 +1201,7 @@ public class SpringApplication {
 	 * @return the environment property prefix
 	 * @since 2.5.0
 	 */
-	public String getEnvironmentPrefix() {
+	public @Nullable String getEnvironmentPrefix() {
 		return this.environmentPrefix;
 	}
 
@@ -1213,7 +1223,7 @@ public class SpringApplication {
 	 * @param applicationContextFactory the factory for the context
 	 * @since 2.4.0
 	 */
-	public void setApplicationContextFactory(ApplicationContextFactory applicationContextFactory) {
+	public void setApplicationContextFactory(@Nullable ApplicationContextFactory applicationContextFactory) {
 		this.applicationContextFactory = (applicationContextFactory != null) ? applicationContextFactory
 				: ApplicationContextFactory.DEFAULT;
 	}
@@ -1424,7 +1434,7 @@ public class SpringApplication {
 	public static void withHook(SpringApplicationHook hook, Runnable action) {
 		withHook(hook, () -> {
 			action.run();
-			return null;
+			return Void.class;
 		});
 	}
 
@@ -1598,7 +1608,7 @@ public class SpringApplication {
 	 */
 	public static class AbandonedRunException extends RuntimeException {
 
-		private final ConfigurableApplicationContext applicationContext;
+		private final @Nullable ConfigurableApplicationContext applicationContext;
 
 		/**
 		 * Create a new {@link AbandonedRunException} instance.
@@ -1613,7 +1623,7 @@ public class SpringApplication {
 		 * @param applicationContext the application context that was available when the
 		 * run was abandoned
 		 */
-		public AbandonedRunException(ConfigurableApplicationContext applicationContext) {
+		public AbandonedRunException(@Nullable ConfigurableApplicationContext applicationContext) {
 			this.applicationContext = applicationContext;
 		}
 
@@ -1622,7 +1632,7 @@ public class SpringApplication {
 		 * {@code null} if no context was available.
 		 * @return the application context
 		 */
-		public ConfigurableApplicationContext getApplicationContext() {
+		public @Nullable ConfigurableApplicationContext getApplicationContext() {
 			return this.applicationContext;
 		}
 
@@ -1642,7 +1652,7 @@ public class SpringApplication {
 		}
 
 		@Override
-		public SpringApplicationRunListener getRunListener(SpringApplication springApplication) {
+		public @Nullable SpringApplicationRunListener getRunListener(SpringApplication springApplication) {
 			return this.used.compareAndSet(false, true) ? this.delegate.getRunListener(springApplication) : null;
 		}
 
@@ -1699,11 +1709,11 @@ public class SpringApplication {
 	 */
 	abstract static class Startup {
 
-		private Duration timeTakenToStarted;
+		private @Nullable Duration timeTakenToStarted;
 
 		protected abstract long startTime();
 
-		protected abstract Long processUptime();
+		protected abstract @Nullable Long processUptime();
 
 		protected abstract String action();
 
@@ -1714,6 +1724,8 @@ public class SpringApplication {
 		}
 
 		Duration timeTakenToStarted() {
+			Assert.state(this.timeTakenToStarted != null,
+					"timeTakenToStarted is not set. Make sure to call started() before this method");
 			return this.timeTakenToStarted;
 		}
 
@@ -1744,7 +1756,7 @@ public class SpringApplication {
 		}
 
 		@Override
-		protected Long processUptime() {
+		protected @Nullable Long processUptime() {
 			try {
 				return ManagementFactory.getRuntimeMXBean().getUptime();
 			}
@@ -1794,7 +1806,7 @@ public class SpringApplication {
 	 * {@link OrderSourceProvider} used to obtain factory method and target type order
 	 * sources. Based on internal {@link DefaultListableBeanFactory} code.
 	 */
-	private class FactoryAwareOrderSourceProvider implements OrderSourceProvider {
+	private static class FactoryAwareOrderSourceProvider implements OrderSourceProvider {
 
 		private final ConfigurableBeanFactory beanFactory;
 
@@ -1806,12 +1818,12 @@ public class SpringApplication {
 		}
 
 		@Override
-		public Object getOrderSource(Object obj) {
+		public @Nullable Object getOrderSource(Object obj) {
 			String beanName = this.instancesToBeanNames.get(obj);
 			return (beanName != null) ? getOrderSource(beanName, obj.getClass()) : null;
 		}
 
-		private Object getOrderSource(String beanName, Class<?> instanceType) {
+		private @Nullable Object getOrderSource(String beanName, Class<?> instanceType) {
 			try {
 				RootBeanDefinition beanDefinition = (RootBeanDefinition) this.beanFactory
 					.getMergedBeanDefinition(beanName);

core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationAotProcessor.java

@@ -59,7 +59,8 @@ public class SpringApplicationAotProcessor extends ContextAotProcessor {
 	protected GenericApplicationContext prepareApplicationContext(Class<?> application) {
 		return new AotProcessorHook(application).run(() -> {
 			Method mainMethod = application.getMethod("main", String[].class);
-			return ReflectionUtils.invokeMethod(mainMethod, null, new Object[] { this.applicationArgs });
+			ReflectionUtils.invokeMethod(mainMethod, null, new Object[] { this.applicationArgs });
+			return Void.class;
 		});
 	}
 
@@ -112,7 +113,7 @@ public class SpringApplicationAotProcessor extends ContextAotProcessor {
 				ApplicationContext context = ex.getApplicationContext();
 				Assert.state(context instanceof GenericApplicationContext,
 						() -> "AOT processing requires a GenericApplicationContext but got a "
-								+ context.getClass().getName());
+								+ ((context != null) ? context.getClass().getName() : "null"));
 				return (GenericApplicationContext) context;
 			}
 			throw new IllegalStateException(

core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationBannerPrinter.java

@@ -23,6 +23,7 @@ import java.io.UnsupportedEncodingException;
 import java.nio.charset.StandardCharsets;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
@@ -45,14 +46,14 @@ class SpringApplicationBannerPrinter {
 
 	private final ResourceLoader resourceLoader;
 
-	private final Banner fallbackBanner;
+	private final @Nullable Banner fallbackBanner;
 
-	SpringApplicationBannerPrinter(ResourceLoader resourceLoader, Banner fallbackBanner) {
+	SpringApplicationBannerPrinter(ResourceLoader resourceLoader, @Nullable Banner fallbackBanner) {
 		this.resourceLoader = resourceLoader;
 		this.fallbackBanner = fallbackBanner;
 	}
 
-	Banner print(Environment environment, Class<?> sourceClass, Log logger) {
+	Banner print(Environment environment, @Nullable Class<?> sourceClass, Log logger) {
 		Banner banner = getBanner(environment);
 		try {
 			logger.info(createStringFromBanner(banner, environment, sourceClass));
@@ -63,7 +64,7 @@ class SpringApplicationBannerPrinter {
 		return new PrintedBanner(banner, sourceClass);
 	}
 
-	Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
+	Banner print(Environment environment, @Nullable Class<?> sourceClass, PrintStream out) {
 		Banner banner = getBanner(environment);
 		banner.printBanner(environment, sourceClass, out);
 		return new PrintedBanner(banner, sourceClass);
@@ -80,7 +81,7 @@ class SpringApplicationBannerPrinter {
 		return DEFAULT_BANNER;
 	}
 
-	private Banner getTextBanner(Environment environment) {
+	private @Nullable Banner getTextBanner(Environment environment) {
 		String location = environment.getProperty(BANNER_LOCATION_PROPERTY, DEFAULT_BANNER_LOCATION);
 		Resource resource = this.resourceLoader.getResource(location);
 		try {
@@ -94,8 +95,8 @@ class SpringApplicationBannerPrinter {
 		return null;
 	}
 
-	private String createStringFromBanner(Banner banner, Environment environment, Class<?> mainApplicationClass)
-			throws UnsupportedEncodingException {
+	private String createStringFromBanner(Banner banner, Environment environment,
+			@Nullable Class<?> mainApplicationClass) throws UnsupportedEncodingException {
 		String charset = environment.getProperty("spring.banner.charset", StandardCharsets.UTF_8.name());
 		ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
 		try (PrintStream out = new PrintStream(byteArrayOutputStream, false, charset)) {
@@ -112,15 +113,15 @@ class SpringApplicationBannerPrinter {
 
 		private final Banner banner;
 
-		private final Class<?> sourceClass;
+		private final @Nullable Class<?> sourceClass;
 
-		PrintedBanner(Banner banner, Class<?> sourceClass) {
+		PrintedBanner(Banner banner, @Nullable Class<?> sourceClass) {
 			this.banner = banner;
 			this.sourceClass = sourceClass;
 		}
 
 		@Override
-		public void printBanner(Environment environment, Class<?> sourceClass, PrintStream out) {
+		public void printBanner(Environment environment, @Nullable Class<?> sourceClass, PrintStream out) {
 			sourceClass = (sourceClass != null) ? sourceClass : this.sourceClass;
 			this.banner.printBanner(environment, sourceClass, out);
 		}
@@ -130,7 +131,7 @@ class SpringApplicationBannerPrinter {
 	static class SpringApplicationBannerPrinterRuntimeHints implements RuntimeHintsRegistrar {
 
 		@Override
-		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 			hints.resources().registerPattern(DEFAULT_BANNER_LOCATION);
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationHook.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Low-level hook that can be used to attach a {@link SpringApplicationRunListener} to a
  * {@link SpringApplication} in order to observe or modify its behavior. Hooks are managed
@@ -34,8 +36,8 @@ public interface SpringApplicationHook {
 	 * Return the {@link SpringApplicationRunListener} that should be hooked into the
 	 * given {@link SpringApplication}.
 	 * @param springApplication the source {@link SpringApplication} instance
-	 * @return the {@link SpringApplicationRunListener} to attach
+	 * @return the {@link SpringApplicationRunListener} to attach or {@code null}
 	 */
-	SpringApplicationRunListener getRunListener(SpringApplication springApplication);
+	@Nullable SpringApplicationRunListener getRunListener(SpringApplication springApplication);
 
 }

core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListener.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.time.Duration;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.core.env.ConfigurableEnvironment;
@@ -80,7 +82,7 @@ public interface SpringApplicationRunListener {
 	 * @param timeTaken the time taken to start the application or {@code null} if unknown
 	 * @since 2.6.0
 	 */
-	default void started(ConfigurableApplicationContext context, Duration timeTaken) {
+	default void started(ConfigurableApplicationContext context, @Nullable Duration timeTaken) {
 	}
 
 	/**
@@ -92,7 +94,7 @@ public interface SpringApplicationRunListener {
 	 * unknown
 	 * @since 2.6.0
 	 */
-	default void ready(ConfigurableApplicationContext context, Duration timeTaken) {
+	default void ready(ConfigurableApplicationContext context, @Nullable Duration timeTaken) {
 	}
 
 	/**
@@ -102,7 +104,7 @@ public interface SpringApplicationRunListener {
 	 * @param exception the failure
 	 * @since 2.0.0
 	 */
-	default void failed(ConfigurableApplicationContext context, Throwable exception) {
+	default void failed(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 	}
 
 }

core/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListeners.java

@@ -21,6 +21,7 @@ import java.util.List;
 import java.util.function.Consumer;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.core.env.ConfigurableEnvironment;
@@ -50,7 +51,7 @@ class SpringApplicationRunListeners {
 		this.applicationStartup = applicationStartup;
 	}
 
-	void starting(ConfigurableBootstrapContext bootstrapContext, Class<?> mainApplicationClass) {
+	void starting(ConfigurableBootstrapContext bootstrapContext, @Nullable Class<?> mainApplicationClass) {
 		doWithListeners("spring.boot.application.starting", (listener) -> listener.starting(bootstrapContext),
 				(step) -> {
 					if (mainApplicationClass != null) {
@@ -80,16 +81,19 @@ class SpringApplicationRunListeners {
 		doWithListeners("spring.boot.application.ready", (listener) -> listener.ready(context, timeTaken));
 	}
 
-	void failed(ConfigurableApplicationContext context, Throwable exception) {
+	void failed(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		doWithListeners("spring.boot.application.failed",
 				(listener) -> callFailedListener(listener, context, exception), (step) -> {
 					step.tag("exception", exception.getClass().toString());
-					step.tag("message", exception.getMessage());
+					String message = exception.getMessage();
+					if (message != null) {
+						step.tag("message", message);
+					}
 				});
 	}
 
-	private void callFailedListener(SpringApplicationRunListener listener, ConfigurableApplicationContext context,
-			Throwable exception) {
+	private void callFailedListener(SpringApplicationRunListener listener,
+			@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		try {
 			listener.failed(context, exception);
 		}
@@ -113,7 +117,7 @@ class SpringApplicationRunListeners {
 	}
 
 	private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction,
-			Consumer<StartupStep> stepAction) {
+			@Nullable Consumer<StartupStep> stepAction) {
 		StartupStep step = this.applicationStartup.start(stepName);
 		this.listeners.forEach(listenerAction);
 		if (stepAction != null) {

core/spring-boot/src/main/java/org/springframework/boot/SpringBootBanner.java

@@ -18,6 +18,8 @@ package org.springframework.boot;
 
 import java.io.PrintStream;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.ansi.AnsiColor;
 import org.springframework.boot.ansi.AnsiOutput;
 import org.springframework.boot.ansi.AnsiStyle;
@@ -44,7 +46,7 @@ class SpringBootBanner implements Banner {
 	private static final int STRAP_LINE_SIZE = 42;
 
 	@Override
-	public void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) {
+	public void printBanner(Environment environment, @Nullable Class<?> sourceClass, PrintStream printStream) {
 		printStream.println();
 		printStream.println(BANNER);
 		String version = String.format(" (v%s)", SpringBootVersion.getVersion());

core/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionHandler.java

@@ -24,6 +24,8 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@link UncaughtExceptionHandler} to suppress handling already logged exceptions and
  * dealing with system exit.
@@ -42,13 +44,13 @@ class SpringBootExceptionHandler implements UncaughtExceptionHandler {
 
 	private static final LoggedExceptionHandlerThreadLocal handler = new LoggedExceptionHandlerThreadLocal();
 
-	private final UncaughtExceptionHandler parent;
+	private final @Nullable UncaughtExceptionHandler parent;
 
 	private final List<Throwable> loggedExceptions = new ArrayList<>();
 
 	private int exitCode = 0;
 
-	SpringBootExceptionHandler(UncaughtExceptionHandler parent) {
+	SpringBootExceptionHandler(@Nullable UncaughtExceptionHandler parent) {
 		this.parent = parent;
 	}
 
@@ -85,7 +87,10 @@ class SpringBootExceptionHandler implements UncaughtExceptionHandler {
 	 * @param ex the source exception
 	 * @return {@code true} if the exception contains a log configuration message
 	 */
-	private boolean isLogConfigurationMessage(Throwable ex) {
+	private boolean isLogConfigurationMessage(@Nullable Throwable ex) {
+		if (ex == null) {
+			return false;
+		}
 		if (ex instanceof InvocationTargetException) {
 			return isLogConfigurationMessage(ex.getCause());
 		}
@@ -100,7 +105,10 @@ class SpringBootExceptionHandler implements UncaughtExceptionHandler {
 		return false;
 	}
 
-	private boolean isRegistered(Throwable ex) {
+	private boolean isRegistered(@Nullable Throwable ex) {
+		if (ex == null) {
+			return false;
+		}
 		if (this.loggedExceptions.contains(ex)) {
 			return true;
 		}

core/spring-boot/src/main/java/org/springframework/boot/StartupInfoLogger.java

@@ -19,6 +19,7 @@ package org.springframework.boot;
 import java.util.concurrent.Callable;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.aot.AotDetector;
 import org.springframework.boot.SpringApplication.Startup;
@@ -39,11 +40,11 @@ import org.springframework.util.StringUtils;
  */
 class StartupInfoLogger {
 
-	private final Class<?> sourceClass;
+	private final @Nullable Class<?> sourceClass;
 
 	private final Environment environment;
 
-	StartupInfoLogger(Class<?> sourceClass, Environment environment) {
+	StartupInfoLogger(@Nullable Class<?> sourceClass, Environment environment) {
 		this.sourceClass = sourceClass;
 		this.environment = environment;
 	}
@@ -153,7 +154,7 @@ class StartupInfoLogger {
 		}
 	}
 
-	private Object callIfPossible(Callable<Object> call) {
+	private @Nullable Object callIfPossible(Callable<Object> call) {
 		try {
 			return call.call();
 		}

core/spring-boot/src/main/java/org/springframework/boot/WebApplicationType.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.aot.hint.TypeReference;
@@ -73,7 +75,7 @@ public enum WebApplicationType {
 	static class WebApplicationTypeRuntimeHints implements RuntimeHintsRegistrar {
 
 		@Override
-		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 			for (String servletIndicatorClass : SERVLET_INDICATOR_CLASSES) {
 				registerTypeIfPresent(servletIndicatorClass, classLoader, hints);
 			}
@@ -82,7 +84,7 @@ public enum WebApplicationType {
 			registerTypeIfPresent(WEBMVC_INDICATOR_CLASS, classLoader, hints);
 		}
 
-		private void registerTypeIfPresent(String typeName, ClassLoader classLoader, RuntimeHints hints) {
+		private void registerTypeIfPresent(String typeName, @Nullable ClassLoader classLoader, RuntimeHints hints) {
 			if (ClassUtils.isPresent(typeName, classLoader)) {
 				hints.reflection().registerType(TypeReference.of(typeName));
 			}

core/spring-boot/src/main/java/org/springframework/boot/admin/SpringApplicationAdminMXBean.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.admin;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * An MBean contract to control and monitor a running {@code SpringApplication} over JMX.
  * Intended for internal use only.
@@ -47,7 +49,7 @@ public interface SpringApplicationAdminMXBean {
 	 * @param key the property key
 	 * @return the property value or {@code null} if it does not exist
 	 */
-	String getProperty(String key);
+	@Nullable String getProperty(String key);
 
 	/**
 	 * Shutdown the application.

core/spring-boot/src/main/java/org/springframework/boot/admin/SpringApplicationAdminMXBeanRegistrar.java

@@ -24,6 +24,7 @@ import javax.management.ObjectName;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.DisposableBean;
@@ -55,6 +56,7 @@ public class SpringApplicationAdminMXBeanRegistrar implements ApplicationContext
 
 	private static final Log logger = LogFactory.getLog(SpringApplicationAdmin.class);
 
+	@SuppressWarnings("NullAway.Init")
 	private ConfigurableApplicationContext applicationContext;
 
 	private Environment environment = new StandardEnvironment();
@@ -89,7 +91,7 @@ public class SpringApplicationAdminMXBeanRegistrar implements ApplicationContext
 	}
 
 	@Override
-	public boolean supportsSourceType(Class<?> sourceType) {
+	public boolean supportsSourceType(@Nullable Class<?> sourceType) {
 		return true;
 	}
 
@@ -139,7 +141,7 @@ public class SpringApplicationAdminMXBeanRegistrar implements ApplicationContext
 		}
 
 		@Override
-		public String getProperty(String key) {
+		public @Nullable String getProperty(String key) {
 			return SpringApplicationAdminMXBeanRegistrar.this.environment.getProperty(key);
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/admin/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Administration support for Spring Boot applications.
  */
+@NullMarked
 package org.springframework.boot.admin;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/ansi/AnsiOutput.java

@@ -20,6 +20,8 @@ import java.io.Console;
 import java.lang.reflect.Method;
 import java.util.Locale;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
@@ -37,9 +39,9 @@ public abstract class AnsiOutput {
 
 	private static Enabled enabled = Enabled.DETECT;
 
-	private static Boolean consoleAvailable;
+	private static @Nullable Boolean consoleAvailable;
 
-	private static Boolean ansiCapable;
+	private static @Nullable Boolean ansiCapable;
 
 	private static final String OPERATING_SYSTEM_NAME = System.getProperty("os.name").toLowerCase(Locale.ENGLISH);
 
@@ -71,7 +73,7 @@ public abstract class AnsiOutput {
 	 * @param consoleAvailable if the console is known to be available or {@code null} to
 	 * use standard detection logic.
 	 */
-	public static void setConsoleAvailable(Boolean consoleAvailable) {
+	public static void setConsoleAvailable(@Nullable Boolean consoleAvailable) {
 		AnsiOutput.consoleAvailable = consoleAvailable;
 	}
 
@@ -133,7 +135,7 @@ public abstract class AnsiOutput {
 		}
 	}
 
-	private static void buildDisabled(StringBuilder sb, Object[] elements) {
+	private static void buildDisabled(StringBuilder sb, @Nullable Object[] elements) {
 		for (Object element : elements) {
 			if (!(element instanceof AnsiElement) && element != null) {
 				sb.append(element);

core/spring-boot/src/main/java/org/springframework/boot/ansi/AnsiPropertySource.java

@@ -23,6 +23,8 @@ import java.util.List;
 import java.util.Set;
 import java.util.function.IntFunction;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.env.PropertyResolver;
 import org.springframework.core.env.PropertySource;
 import org.springframework.util.StringUtils;
@@ -73,7 +75,7 @@ public class AnsiPropertySource extends PropertySource<AnsiElement> {
 	}
 
 	@Override
-	public Object getProperty(String name) {
+	public @Nullable Object getProperty(String name) {
 		if (StringUtils.hasLength(name)) {
 			for (Mapping mapping : MAPPINGS) {
 				String prefix = mapping.getPrefix();
@@ -104,7 +106,7 @@ public class AnsiPropertySource extends PropertySource<AnsiElement> {
 			return this.prefix;
 		}
 
-		abstract AnsiElement getElement(String postfix);
+		abstract @Nullable AnsiElement getElement(String postfix);
 
 	}
 
@@ -121,7 +123,7 @@ public class AnsiPropertySource extends PropertySource<AnsiElement> {
 		}
 
 		@Override
-		AnsiElement getElement(String postfix) {
+		@Nullable AnsiElement getElement(String postfix) {
 			for (Enum<?> candidate : this.enums) {
 				if (candidate.name().equals(postfix)) {
 					return (AnsiElement) candidate;
@@ -145,7 +147,7 @@ public class AnsiPropertySource extends PropertySource<AnsiElement> {
 		}
 
 		@Override
-		AnsiElement getElement(String postfix) {
+		@Nullable AnsiElement getElement(String postfix) {
 			if (containsOnlyDigits(postfix)) {
 				try {
 					return this.factory.apply(Integer.parseInt(postfix));

core/spring-boot/src/main/java/org/springframework/boot/ansi/package-info.java

@@ -19,4 +19,7 @@
  *
  * @see org.springframework.boot.ansi.AnsiOutput
  */
+@NullMarked
 package org.springframework.boot.ansi;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/availability/ApplicationAvailability.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.availability;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationContext;
 
 /**
@@ -67,7 +69,7 @@ public interface ApplicationAvailability {
 	 * published yet
 	 * @see #getState(Class, AvailabilityState)
 	 */
-	<S extends AvailabilityState> S getState(Class<S> stateType);
+	<S extends AvailabilityState> @Nullable S getState(Class<S> stateType);
 
 	/**
 	 * Return the last {@link AvailabilityChangeEvent} received for a given state type.
@@ -76,6 +78,6 @@ public interface ApplicationAvailability {
 	 * @return the readiness state or {@code null} if no event of the given type has been
 	 * published yet
 	 */
-	<S extends AvailabilityState> AvailabilityChangeEvent<S> getLastChangeEvent(Class<S> stateType);
+	<S extends AvailabilityState> @Nullable AvailabilityChangeEvent<S> getLastChangeEvent(Class<S> stateType);
 
 }

core/spring-boot/src/main/java/org/springframework/boot/availability/ApplicationAvailabilityBean.java

@@ -21,6 +21,7 @@ import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationListener;
@@ -59,14 +60,14 @@ public class ApplicationAvailabilityBean
 	}
 
 	@Override
-	public <S extends AvailabilityState> S getState(Class<S> stateType) {
+	public <S extends AvailabilityState> @Nullable S getState(Class<S> stateType) {
 		AvailabilityChangeEvent<S> event = getLastChangeEvent(stateType);
 		return (event != null) ? event.getState() : null;
 	}
 
 	@Override
 	@SuppressWarnings("unchecked")
-	public <S extends AvailabilityState> AvailabilityChangeEvent<S> getLastChangeEvent(Class<S> stateType) {
+	public <S extends AvailabilityState> @Nullable AvailabilityChangeEvent<S> getLastChangeEvent(Class<S> stateType) {
 		return (AvailabilityChangeEvent<S>) this.events.get(stateType);
 	}
 
@@ -89,7 +90,7 @@ public class ApplicationAvailabilityBean
 		return message;
 	}
 
-	private String getSourceDescription(Object source) {
+	private String getSourceDescription(@Nullable Object source) {
 		if (source == null || source instanceof ApplicationEventPublisher) {
 			return "";
 		}

core/spring-boot/src/main/java/org/springframework/boot/availability/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Support for describing the availability of Spring Boot applications.
  */
+@NullMarked
 package org.springframework.boot.availability;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/builder/ParentContextCloserApplicationListener.java

@@ -40,8 +40,9 @@ import org.springframework.util.ObjectUtils;
 public class ParentContextCloserApplicationListener
 		implements ApplicationListener<ParentContextAvailableEvent>, ApplicationContextAware, Ordered {
 
-	private final int order = Ordered.LOWEST_PRECEDENCE - 10;
+	private static final int order = Ordered.LOWEST_PRECEDENCE - 10;
 
+	@SuppressWarnings("NullAway.Init")
 	private ApplicationContext context;
 
 	@Override

core/spring-boot/src/main/java/org/springframework/boot/builder/SpringApplicationBuilder.java

@@ -27,6 +27,8 @@ import java.util.Properties;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory;
 import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.boot.ApplicationContextFactory;
@@ -44,6 +46,7 @@ import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.metrics.ApplicationStartup;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -76,9 +79,9 @@ public class SpringApplicationBuilder {
 
 	private final SpringApplication application;
 
-	private volatile ConfigurableApplicationContext context;
+	private volatile @Nullable ConfigurableApplicationContext context;
 
-	private SpringApplicationBuilder parent;
+	private @Nullable SpringApplicationBuilder parent;
 
 	private final AtomicBoolean running = new AtomicBoolean();
 
@@ -86,7 +89,7 @@ public class SpringApplicationBuilder {
 
 	private final Map<String, Object> defaultProperties = new LinkedHashMap<>();
 
-	private ConfigurableEnvironment environment;
+	private @Nullable ConfigurableEnvironment environment;
 
 	private Set<String> additionalProfiles = new LinkedHashSet<>();
 
@@ -98,7 +101,7 @@ public class SpringApplicationBuilder {
 		this(null, sources);
 	}
 
-	public SpringApplicationBuilder(ResourceLoader resourceLoader, Class<?>... sources) {
+	public SpringApplicationBuilder(@Nullable ResourceLoader resourceLoader, Class<?>... sources) {
 		this.application = createSpringApplication(resourceLoader, sources);
 	}
 
@@ -111,15 +114,15 @@ public class SpringApplicationBuilder {
 	 * @return the {@link SpringApplication} instance
 	 * @since 2.6.0
 	 */
-	protected SpringApplication createSpringApplication(ResourceLoader resourceLoader, Class<?>... sources) {
+	protected SpringApplication createSpringApplication(@Nullable ResourceLoader resourceLoader, Class<?>... sources) {
 		return new SpringApplication(resourceLoader, sources);
 	}
 
 	/**
 	 * Accessor for the current application context.
-	 * @return the current application context (or null if not yet running)
+	 * @return the current application context (or {@code null} if not yet running)
 	 */
-	public ConfigurableApplicationContext context() {
+	public @Nullable ConfigurableApplicationContext context() {
 		return this.context;
 	}
 
@@ -140,15 +143,19 @@ public class SpringApplicationBuilder {
 	 */
 	public ConfigurableApplicationContext run(String... args) {
 		if (this.running.get()) {
+			ConfigurableApplicationContext context = this.context;
+			Assert.state(context != null, "No context set");
 			// If already created we just return the existing context
-			return this.context;
+			return context;
 		}
 		configureAsChildIfNecessary(args);
 		if (this.running.compareAndSet(false, true)) {
 			// If not already running copy the sources over and then run.
 			this.context = build().run(args);
 		}
-		return this.context;
+		ConfigurableApplicationContext context = this.context;
+		Assert.state(context != null, "No context set");
+		return context;
 	}
 
 	private void configureAsChildIfNecessary(String... args) {
@@ -519,10 +526,10 @@ public class SpringApplicationBuilder {
 
 	/**
 	 * Environment for the application context.
-	 * @param environment the environment to set.
+	 * @param environment the environment to set
 	 * @return the current builder
 	 */
-	public SpringApplicationBuilder environment(ConfigurableEnvironment environment) {
+	public SpringApplicationBuilder environment(@Nullable ConfigurableEnvironment environment) {
 		this.application.setEnvironment(environment);
 		this.environment = environment;
 		return this;

core/spring-boot/src/main/java/org/springframework/boot/builder/package-info.java

@@ -20,4 +20,7 @@
  *
  * @see org.springframework.boot.builder.SpringApplicationBuilder
  */
+@NullMarked
 package org.springframework.boot.builder;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/cloud/CloudFoundryVcapEnvironmentPostProcessor.java

@@ -23,6 +23,7 @@ import java.util.Map;
 import java.util.Properties;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor;
@@ -165,13 +166,13 @@ public class CloudFoundryVcapEnvironmentPostProcessor implements EnvironmentPost
 		return properties;
 	}
 
-	private void extractPropertiesFromApplication(Properties properties, Map<String, Object> map) {
+	private void extractPropertiesFromApplication(Properties properties, @Nullable Map<String, Object> map) {
 		if (map != null) {
 			flatten(properties, map, "");
 		}
 	}
 
-	private void extractPropertiesFromServices(Properties properties, Map<String, Object> map) {
+	private void extractPropertiesFromServices(Properties properties, @Nullable Map<String, Object> map) {
 		if (map != null) {
 			for (Object services : map.values()) {
 				@SuppressWarnings("unchecked")
@@ -190,7 +191,7 @@ public class CloudFoundryVcapEnvironmentPostProcessor implements EnvironmentPost
 	}
 
 	@SuppressWarnings("unchecked")
-	private void flatten(Properties properties, Map<String, Object> input, String path) {
+	private void flatten(Properties properties, Map<String, Object> input, @Nullable String path) {
 		input.forEach((key, value) -> {
 			String name = getPropertyName(path, key);
 			if (value instanceof Map) {
@@ -218,7 +219,7 @@ public class CloudFoundryVcapEnvironmentPostProcessor implements EnvironmentPost
 		});
 	}
 
-	private String getPropertyName(String path, String key) {
+	private String getPropertyName(@Nullable String path, String key) {
 		if (!StringUtils.hasText(path)) {
 			return key;
 		}

core/spring-boot/src/main/java/org/springframework/boot/cloud/CloudPlatform.java

@@ -19,6 +19,8 @@ package org.springframework.boot.cloud;
 import java.util.Arrays;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.EnumerablePropertySource;
@@ -198,7 +200,7 @@ public enum CloudPlatform {
 		return isEnforced(binder.bind(PROPERTY_NAME, String.class).orElse(null));
 	}
 
-	private boolean isEnforced(String platform) {
+	private boolean isEnforced(@Nullable String platform) {
 		return name().equalsIgnoreCase(platform);
 	}
 
@@ -225,7 +227,7 @@ public enum CloudPlatform {
 	 * @param environment the environment
 	 * @return the {@link CloudPlatform} or {@code null}
 	 */
-	public static CloudPlatform getActive(Environment environment) {
+	public static @Nullable CloudPlatform getActive(@Nullable Environment environment) {
 		if (environment != null) {
 			for (CloudPlatform cloudPlatform : values()) {
 				if (cloudPlatform.isActive(environment)) {

core/spring-boot/src/main/java/org/springframework/boot/cloud/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Low level support for Cloud deployments.
  */
+@NullMarked
 package org.springframework.boot.cloud;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/ApplicationPidFileWriter.java

@@ -26,6 +26,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
 import org.springframework.boot.context.event.ApplicationPreparedEvent;
@@ -163,7 +164,7 @@ public class ApplicationPidFileWriter implements ApplicationListener<SpringAppli
 		return Boolean.parseBoolean(value);
 	}
 
-	private String getProperty(SpringApplicationEvent event, List<Property> candidates) {
+	private @Nullable String getProperty(SpringApplicationEvent event, List<Property> candidates) {
 		for (Property candidate : candidates) {
 			String value = candidate.getValue(event);
 			if (value != null) {
@@ -194,7 +195,7 @@ public class ApplicationPidFileWriter implements ApplicationListener<SpringAppli
 	 */
 	private interface Property {
 
-		String getValue(SpringApplicationEvent event);
+		@Nullable String getValue(SpringApplicationEvent event);
 
 	}
 
@@ -213,7 +214,7 @@ public class ApplicationPidFileWriter implements ApplicationListener<SpringAppli
 		}
 
 		@Override
-		public String getValue(SpringApplicationEvent event) {
+		public @Nullable String getValue(SpringApplicationEvent event) {
 			Environment environment = getEnvironment(event);
 			if (environment == null) {
 				return null;
@@ -221,7 +222,7 @@ public class ApplicationPidFileWriter implements ApplicationListener<SpringAppli
 			return environment.getProperty(this.prefix + this.key);
 		}
 
-		private Environment getEnvironment(SpringApplicationEvent event) {
+		private @Nullable Environment getEnvironment(SpringApplicationEvent event) {
 			if (event instanceof ApplicationEnvironmentPreparedEvent environmentPreparedEvent) {
 				return environmentPreparedEvent.getEnvironment();
 			}
@@ -248,7 +249,7 @@ public class ApplicationPidFileWriter implements ApplicationListener<SpringAppli
 		}
 
 		@Override
-		public String getValue(SpringApplicationEvent event) {
+		public @Nullable String getValue(SpringApplicationEvent event) {
 			return SystemProperties.get(this.properties);
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/context/ConfigurationWarningsApplicationContextInitializer.java

@@ -25,6 +25,7 @@ import java.util.Set;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
@@ -118,7 +119,7 @@ public class ConfigurationWarningsApplicationContextInitializer
 		 * @param registry the {@link BeanDefinitionRegistry}
 		 * @return a warning message or {@code null}
 		 */
-		String getWarning(BeanDefinitionRegistry registry);
+		@Nullable String getWarning(BeanDefinitionRegistry registry);
 
 	}
 
@@ -137,7 +138,7 @@ public class ConfigurationWarningsApplicationContextInitializer
 		}
 
 		@Override
-		public String getWarning(BeanDefinitionRegistry registry) {
+		public @Nullable String getWarning(BeanDefinitionRegistry registry) {
 			Set<String> scannedPackages = getComponentScanningPackages(registry);
 			List<String> problematicPackages = getProblematicPackages(scannedPackages);
 			if (problematicPackages.isEmpty()) {
@@ -172,13 +173,13 @@ public class ConfigurationWarningsApplicationContextInitializer
 			}
 		}
 
-		private void addPackages(Set<String> packages, String[] values) {
+		private void addPackages(Set<String> packages, String @Nullable [] values) {
 			if (values != null) {
 				Collections.addAll(packages, values);
 			}
 		}
 
-		private void addClasses(Set<String> packages, String[] values) {
+		private void addClasses(Set<String> packages, String @Nullable [] values) {
 			if (values != null) {
 				for (String value : values) {
 					packages.add(ClassUtils.getPackageName(value));
@@ -196,14 +197,14 @@ public class ConfigurationWarningsApplicationContextInitializer
 			return problematicPackages;
 		}
 
-		private boolean isProblematicPackage(String scannedPackage) {
+		private boolean isProblematicPackage(@Nullable String scannedPackage) {
 			if (scannedPackage == null || scannedPackage.isEmpty()) {
 				return true;
 			}
 			return PROBLEM_PACKAGES.contains(scannedPackage);
 		}
 
-		private String getDisplayName(String scannedPackage) {
+		private String getDisplayName(@Nullable String scannedPackage) {
 			if (scannedPackage == null || scannedPackage.isEmpty()) {
 				return "the default package";
 			}

core/spring-boot/src/main/java/org/springframework/boot/context/TypeExcludeFilter.java

@@ -19,6 +19,8 @@ package org.springframework.boot.context;
 import java.io.IOException;
 import java.util.Collection;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
@@ -49,9 +51,10 @@ import org.springframework.core.type.filter.TypeFilter;
  */
 public class TypeExcludeFilter implements TypeFilter, BeanFactoryAware {
 
+	@SuppressWarnings("NullAway.Init")
 	private BeanFactory beanFactory;
 
-	private Collection<TypeExcludeFilter> delegates;
+	private @Nullable Collection<TypeExcludeFilter> delegates;
 
 	@Override
 	public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
@@ -81,7 +84,7 @@ public class TypeExcludeFilter implements TypeFilter, BeanFactoryAware {
 	}
 
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		throw new IllegalStateException("TypeExcludeFilter " + getClass() + " has not implemented equals");
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/annotation/Configurations.java

@@ -30,6 +30,8 @@ import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.ImportSelector;
@@ -61,11 +63,11 @@ public abstract class Configurations {
 	private static final Comparator<Object> COMPARATOR = OrderComparator.INSTANCE
 		.thenComparing((other) -> other.getClass().getName());
 
-	private final UnaryOperator<Collection<Class<?>>> sorter;
+	private final @Nullable UnaryOperator<Collection<Class<?>>> sorter;
 
 	private final Set<Class<?>> classes;
 
-	private final Function<Class<?>, String> beanNameGenerator;
+	private final @Nullable Function<Class<?>, String> beanNameGenerator;
 
 	/**
 	 * Create a new {@link Configurations} instance.
@@ -85,7 +87,7 @@ public abstract class Configurations {
 	 * @param beanNameGenerator an optional function used to generate the bean name
 	 * @since 3.4.0
 	 */
-	protected Configurations(UnaryOperator<Collection<Class<?>>> sorter, Collection<Class<?>> classes,
+	protected Configurations(@Nullable UnaryOperator<Collection<Class<?>>> sorter, Collection<Class<?>> classes,
 			Function<Class<?>, String> beanNameGenerator) {
 		Assert.notNull(classes, "'classes' must not be null");
 		this.sorter = (sorter != null) ? sorter : UnaryOperator.identity();
@@ -127,7 +129,7 @@ public abstract class Configurations {
 	 * @return the bean name
 	 * @since 3.4.0
 	 */
-	public String getBeanName(Class<?> beanClass) {
+	public @Nullable String getBeanName(Class<?> beanClass) {
 		return (this.beanNameGenerator != null) ? this.beanNameGenerator.apply(beanClass) : null;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/annotation/ImportCandidates.java

@@ -27,6 +27,8 @@ import java.util.Enumeration;
 import java.util.Iterator;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.io.UrlResource;
 import org.springframework.util.Assert;
 
@@ -76,7 +78,7 @@ public final class ImportCandidates implements Iterable<String> {
 	 * @param classLoader class loader to use for loading
 	 * @return list of names of annotated classes
 	 */
-	public static ImportCandidates load(Class<?> annotation, ClassLoader classLoader) {
+	public static ImportCandidates load(Class<?> annotation, @Nullable ClassLoader classLoader) {
 		Assert.notNull(annotation, "'annotation' must not be null");
 		ClassLoader classLoaderToUse = decideClassloader(classLoader);
 		String location = String.format(LOCATION, annotation.getName());
@@ -89,7 +91,7 @@ public final class ImportCandidates implements Iterable<String> {
 		return new ImportCandidates(importCandidates);
 	}
 
-	private static ClassLoader decideClassloader(ClassLoader classLoader) {
+	private static ClassLoader decideClassloader(@Nullable ClassLoader classLoader) {
 		if (classLoader == null) {
 			return ImportCandidates.class.getClassLoader();
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/annotation/package-info.java

@@ -18,4 +18,7 @@
  * Classes related to Spring's {@link org.springframework.context.ApplicationContext}
  * annotations.
  */
+@NullMarked
 package org.springframework.boot.context.annotation;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigData.java

@@ -25,6 +25,8 @@ import java.util.List;
 import java.util.Set;
 import java.util.function.Consumer;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.env.Environment;
 import org.springframework.core.env.PropertySource;
 import org.springframework.util.Assert;
@@ -120,7 +122,7 @@ public final class ConfigData {
 		 * @param propertySource the property source
 		 * @return the options to apply
 		 */
-		Options get(PropertySource<?> propertySource);
+		@Nullable Options get(PropertySource<?> propertySource);
 
 		/**
 		 * Create a new {@link PropertySourceOptions} instance that always returns the

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataActivationContext.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.cloud.CloudPlatform;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.core.env.Environment;
@@ -29,9 +31,9 @@ import org.springframework.core.style.ToStringCreator;
  */
 class ConfigDataActivationContext {
 
-	private final CloudPlatform cloudPlatform;
+	private final @Nullable CloudPlatform cloudPlatform;
 
-	private final Profiles profiles;
+	private final @Nullable Profiles profiles;
 
 	/**
 	 * Create a new {@link ConfigDataActivationContext} instance before any profiles have
@@ -50,12 +52,12 @@ class ConfigDataActivationContext {
 	 * @param cloudPlatform the cloud platform
 	 * @param profiles the profiles
 	 */
-	ConfigDataActivationContext(CloudPlatform cloudPlatform, Profiles profiles) {
+	ConfigDataActivationContext(@Nullable CloudPlatform cloudPlatform, Profiles profiles) {
 		this.cloudPlatform = cloudPlatform;
 		this.profiles = profiles;
 	}
 
-	private CloudPlatform deduceCloudPlatform(Environment environment, Binder binder) {
+	private @Nullable CloudPlatform deduceCloudPlatform(Environment environment, Binder binder) {
 		for (CloudPlatform candidate : CloudPlatform.values()) {
 			if (candidate.isEnforced(binder)) {
 				return candidate;
@@ -77,7 +79,7 @@ class ConfigDataActivationContext {
 	 * Return the active {@link CloudPlatform} or {@code null}.
 	 * @return the active cloud platform
 	 */
-	CloudPlatform getCloudPlatform() {
+	@Nullable CloudPlatform getCloudPlatform() {
 		return this.cloudPlatform;
 	}
 
@@ -85,7 +87,7 @@ class ConfigDataActivationContext {
 	 * Return profile information if it is available.
 	 * @return profile information or {@code null}
 	 */
-	Profiles getProfiles() {
+	@Nullable Profiles getProfiles() {
 		return this.profiles;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironment.java

@@ -24,6 +24,7 @@ import java.util.List;
 import java.util.Set;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.BootstrapRegistry.InstanceSupplier;
 import org.springframework.boot.BootstrapRegistry.Scope;
@@ -43,6 +44,7 @@ import org.springframework.core.env.PropertySource;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.core.log.LogMessage;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -137,7 +139,7 @@ class ConfigDataEnvironment {
 	 */
 	ConfigDataEnvironment(DeferredLogFactory logFactory, ConfigurableBootstrapContext bootstrapContext,
 			ConfigurableEnvironment environment, ResourceLoader resourceLoader, Collection<String> additionalProfiles,
-			ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
+			@Nullable ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
 		Binder binder = Binder.get(environment);
 		this.logFactory = logFactory;
 		this.logger = logFactory.getLog(getClass());
@@ -321,7 +323,7 @@ class ConfigDataEnvironment {
 	}
 
 	private void registerBootstrapBinder(ConfigDataEnvironmentContributors contributors,
-			ConfigDataActivationContext activationContext, BinderOption... binderOptions) {
+			@Nullable ConfigDataActivationContext activationContext, BinderOption... binderOptions) {
 		this.bootstrapContext.register(Binder.class,
 				InstanceSupplier.from(() -> contributors.getBinder(activationContext, binderOptions))
 					.withScope(Scope.PROTOTYPE));
@@ -336,6 +338,7 @@ class ConfigDataEnvironment {
 		applyContributor(contributors, activationContext, propertySources);
 		DefaultPropertiesPropertySource.moveToEnd(propertySources);
 		Profiles profiles = activationContext.getProfiles();
+		Assert.state(profiles != null, "'profiles' must not be null");
 		this.logger.trace(LogMessage.format("Setting default profiles: %s", profiles.getDefault()));
 		this.environment.setDefaultProfiles(StringUtils.toStringArray(profiles.getDefault()));
 		this.logger.trace(LogMessage.format("Setting active profiles: %s", profiles.getActive()));

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentContributor.java

@@ -26,6 +26,8 @@ import java.util.NoSuchElementException;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.context.properties.bind.PlaceholdersResolver;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
@@ -33,6 +35,7 @@ import org.springframework.boot.origin.OriginLookup;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.env.Environment;
 import org.springframework.core.env.PropertySource;
+import org.springframework.lang.Contract;
 import org.springframework.util.CollectionUtils;
 
 /**
@@ -58,17 +61,17 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	private static final ConfigData.Options EMPTY_LOCATION_OPTIONS = ConfigData.Options
 		.of(ConfigData.Option.IGNORE_IMPORTS);
 
-	private final ConfigDataLocation location;
+	private final @Nullable ConfigDataLocation location;
 
-	private final ConfigDataResource resource;
+	private final @Nullable ConfigDataResource resource;
 
 	private final boolean fromProfileSpecificImport;
 
-	private final PropertySource<?> propertySource;
+	private final @Nullable PropertySource<?> propertySource;
 
-	private final ConfigurationPropertySource configurationPropertySource;
+	private final @Nullable ConfigurationPropertySource configurationPropertySource;
 
-	private final ConfigDataProperties properties;
+	private final @Nullable ConfigDataProperties properties;
 
 	private final ConfigData.Options configDataOptions;
 
@@ -93,10 +96,12 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 * @param children the children of this contributor at each {@link ImportPhase}
 	 * @param conversionService the conversion service to use
 	 */
-	ConfigDataEnvironmentContributor(Kind kind, ConfigDataLocation location, ConfigDataResource resource,
-			boolean fromProfileSpecificImport, PropertySource<?> propertySource,
-			ConfigurationPropertySource configurationPropertySource, ConfigDataProperties properties,
-			ConfigData.Options configDataOptions, Map<ImportPhase, List<ConfigDataEnvironmentContributor>> children,
+	ConfigDataEnvironmentContributor(Kind kind, @Nullable ConfigDataLocation location,
+			@Nullable ConfigDataResource resource, boolean fromProfileSpecificImport,
+			@Nullable PropertySource<?> propertySource,
+			@Nullable ConfigurationPropertySource configurationPropertySource,
+			@Nullable ConfigDataProperties properties, ConfigData.@Nullable Options configDataOptions,
+			@Nullable Map<ImportPhase, List<ConfigDataEnvironmentContributor>> children,
 			ConversionService conversionService) {
 		this.kind = kind;
 		this.location = location;
@@ -118,7 +123,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 		return this.kind;
 	}
 
-	ConfigDataLocation getLocation() {
+	@Nullable ConfigDataLocation getLocation() {
 		return this.location;
 	}
 
@@ -127,7 +132,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 * @param activationContext the activation context
 	 * @return if the contributor is active
 	 */
-	boolean isActive(ConfigDataActivationContext activationContext) {
+	boolean isActive(@Nullable ConfigDataActivationContext activationContext) {
 		if (this.kind == Kind.UNBOUND_IMPORT) {
 			return false;
 		}
@@ -138,7 +143,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 * Return the resource that contributed this instance.
 	 * @return the resource or {@code null}
 	 */
-	ConfigDataResource getResource() {
+	@Nullable ConfigDataResource getResource() {
 		return this.resource;
 	}
 
@@ -154,7 +159,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 * Return the property source for this contributor.
 	 * @return the property source or {@code null}
 	 */
-	PropertySource<?> getPropertySource() {
+	@Nullable PropertySource<?> getPropertySource() {
 		return this.propertySource;
 	}
 
@@ -162,7 +167,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 * Return the configuration property source for this contributor.
 	 * @return the configuration property source or {@code null}
 	 */
-	ConfigurationPropertySource getConfigurationPropertySource() {
+	@Nullable ConfigurationPropertySource getConfigurationPropertySource() {
 		return this.configurationPropertySource;
 	}
 
@@ -239,7 +244,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 * @return a new contributor instance
 	 */
 	ConfigDataEnvironmentContributor withBoundProperties(Iterable<ConfigDataEnvironmentContributor> contributors,
-			ConfigDataActivationContext activationContext) {
+			@Nullable ConfigDataActivationContext activationContext) {
 		Iterable<ConfigurationPropertySource> sources = Collections.singleton(getConfigurationPropertySource());
 		PlaceholdersResolver placeholdersResolver = new ConfigDataEnvironmentContributorPlaceholdersResolver(
 				contributors, activationContext, this, true, this.conversionService);
@@ -305,7 +310,8 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 		return contributor;
 	}
 
-	private boolean hasAnyProfileSpecificChildren(List<ConfigDataEnvironmentContributor> contributors) {
+	@Contract("null -> false")
+	private boolean hasAnyProfileSpecificChildren(@Nullable List<ConfigDataEnvironmentContributor> contributors) {
 		if (CollectionUtils.isEmpty(contributors)) {
 			return false;
 		}
@@ -441,7 +447,8 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 				propertySource, asConfigurationPropertySource(propertySource), null, options, null, conversionService);
 	}
 
-	private static ConfigurationPropertySource asConfigurationPropertySource(PropertySource<?> propertySource) {
+	private static @Nullable ConfigurationPropertySource asConfigurationPropertySource(
+			PropertySource<?> propertySource) {
 		ConfigurationPropertySource configurationPropertySource = ConfigurationPropertySource.from(propertySource);
 		if (configurationPropertySource != null && propertySource instanceof OriginLookup<?> originLookup) {
 			configurationPropertySource = configurationPropertySource.withPrefix(originLookup.getPrefix());
@@ -521,7 +528,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 		 * @param activationContext the activation context
 		 * @return the import phase
 		 */
-		static ImportPhase get(ConfigDataActivationContext activationContext) {
+		static ImportPhase get(@Nullable ConfigDataActivationContext activationContext) {
 			if (activationContext != null && activationContext.getProfiles() != null) {
 				return AFTER_PROFILE_ACTIVATION;
 			}
@@ -535,13 +542,13 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 	 */
 	private final class ContributorIterator implements Iterator<ConfigDataEnvironmentContributor> {
 
-		private ImportPhase phase;
+		private @Nullable ImportPhase phase;
 
 		private Iterator<ConfigDataEnvironmentContributor> children;
 
 		private Iterator<ConfigDataEnvironmentContributor> current;
 
-		private ConfigDataEnvironmentContributor next;
+		private @Nullable ConfigDataEnvironmentContributor next;
 
 		private ContributorIterator() {
 			this.phase = ImportPhase.AFTER_PROFILE_ACTIVATION;
@@ -564,7 +571,7 @@ class ConfigDataEnvironmentContributor implements Iterable<ConfigDataEnvironment
 			return next;
 		}
 
-		private ConfigDataEnvironmentContributor fetchIfNecessary() {
+		private @Nullable ConfigDataEnvironmentContributor fetchIfNecessary() {
 			if (this.next != null) {
 				return this.next;
 			}

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentContributorPlaceholdersResolver.java

@@ -16,12 +16,15 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.config.ConfigDataEnvironmentContributor.Kind;
 import org.springframework.boot.context.properties.bind.PlaceholdersResolver;
 import org.springframework.boot.origin.Origin;
 import org.springframework.boot.origin.OriginLookup;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.env.PropertySource;
+import org.springframework.util.Assert;
 import org.springframework.util.PropertyPlaceholderHelper;
 import org.springframework.util.SystemPropertyUtils;
 
@@ -37,19 +40,20 @@ class ConfigDataEnvironmentContributorPlaceholdersResolver implements Placeholde
 
 	private final Iterable<ConfigDataEnvironmentContributor> contributors;
 
-	private final ConfigDataActivationContext activationContext;
+	private final @Nullable ConfigDataActivationContext activationContext;
 
 	private final boolean failOnResolveFromInactiveContributor;
 
 	private final PropertyPlaceholderHelper helper;
 
-	private final ConfigDataEnvironmentContributor activeContributor;
+	private final @Nullable ConfigDataEnvironmentContributor activeContributor;
 
 	private final ConversionService conversionService;
 
 	ConfigDataEnvironmentContributorPlaceholdersResolver(Iterable<ConfigDataEnvironmentContributor> contributors,
-			ConfigDataActivationContext activationContext, ConfigDataEnvironmentContributor activeContributor,
-			boolean failOnResolveFromInactiveContributor, ConversionService conversionService) {
+			@Nullable ConfigDataActivationContext activationContext,
+			@Nullable ConfigDataEnvironmentContributor activeContributor, boolean failOnResolveFromInactiveContributor,
+			ConversionService conversionService) {
 		this.contributors = contributors;
 		this.activationContext = activationContext;
 		this.activeContributor = activeContributor;
@@ -61,14 +65,14 @@ class ConfigDataEnvironmentContributorPlaceholdersResolver implements Placeholde
 	}
 
 	@Override
-	public Object resolvePlaceholders(Object value) {
+	public @Nullable Object resolvePlaceholders(@Nullable Object value) {
 		if (value instanceof String string) {
 			return this.helper.replacePlaceholders(string, this::resolvePlaceholder);
 		}
 		return value;
 	}
 
-	private String resolvePlaceholder(String placeholder) {
+	private @Nullable String resolvePlaceholder(String placeholder) {
 		Object result = null;
 		for (ConfigDataEnvironmentContributor contributor : this.contributors) {
 			PropertySource<?> propertySource = contributor.getPropertySource();
@@ -76,6 +80,7 @@ class ConfigDataEnvironmentContributorPlaceholdersResolver implements Placeholde
 			if (value != null && !isActive(contributor)) {
 				if (this.failOnResolveFromInactiveContributor) {
 					ConfigDataResource resource = contributor.getResource();
+					Assert.state(propertySource != null, "'propertySource' can't be null here");
 					Origin origin = OriginLookup.getOrigin(propertySource, placeholder);
 					throw new InactiveConfigDataAccessException(propertySource, resource, placeholder, origin);
 				}
@@ -97,7 +102,7 @@ class ConfigDataEnvironmentContributorPlaceholdersResolver implements Placeholde
 			.isActive(this.activationContext);
 	}
 
-	private String convertValueIfNecessary(Object value) {
+	private @Nullable String convertValueIfNecessary(Object value) {
 		return (value instanceof String string) ? string : this.conversionService.convert(value, String.class);
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentContributors.java

@@ -27,6 +27,7 @@ import java.util.Set;
 import java.util.function.Predicate;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.ConfigurableBootstrapContext;
 import org.springframework.boot.context.config.ConfigDataEnvironmentContributor.ImportPhase;
@@ -102,7 +103,7 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 	 * imports have been processed
 	 */
 	ConfigDataEnvironmentContributors withProcessedImports(ConfigDataImporter importer,
-			ConfigDataActivationContext activationContext) {
+			@Nullable ConfigDataActivationContext activationContext) {
 		ImportPhase importPhase = ImportPhase.get(activationContext);
 		this.logger.trace(LogMessage.format("Processing imports for phase %s. %s", importPhase,
 				(activationContext != null) ? activationContext : "no activation context"));
@@ -152,8 +153,8 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 		return this.bootstrapContext;
 	}
 
-	private ConfigDataEnvironmentContributor getNextToProcess(ConfigDataEnvironmentContributors contributors,
-			ConfigDataActivationContext activationContext, ImportPhase importPhase) {
+	private @Nullable ConfigDataEnvironmentContributor getNextToProcess(ConfigDataEnvironmentContributors contributors,
+			@Nullable ConfigDataActivationContext activationContext, ImportPhase importPhase) {
 		for (ConfigDataEnvironmentContributor contributor : contributors.getRoot()) {
 			if (contributor.getKind() == Kind.UNBOUND_IMPORT
 					|| isActiveWithUnprocessedImports(activationContext, importPhase, contributor)) {
@@ -163,7 +164,7 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 		return null;
 	}
 
-	private boolean isActiveWithUnprocessedImports(ConfigDataActivationContext activationContext,
+	private boolean isActiveWithUnprocessedImports(@Nullable ConfigDataActivationContext activationContext,
 			ImportPhase importPhase, ConfigDataEnvironmentContributor contributor) {
 		return contributor.isActive(activationContext) && contributor.hasUnprocessedImports(importPhase);
 	}
@@ -203,7 +204,7 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 	 * @param options binder options to apply
 	 * @return a binder instance
 	 */
-	Binder getBinder(ConfigDataActivationContext activationContext, BinderOption... options) {
+	Binder getBinder(@Nullable ConfigDataActivationContext activationContext, BinderOption... options) {
 		return getBinder(activationContext, NO_CONTRIBUTOR_FILTER, options);
 	}
 
@@ -214,8 +215,8 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 	 * @param options binder options to apply
 	 * @return a binder instance
 	 */
-	Binder getBinder(ConfigDataActivationContext activationContext, Predicate<ConfigDataEnvironmentContributor> filter,
-			BinderOption... options) {
+	Binder getBinder(@Nullable ConfigDataActivationContext activationContext,
+			Predicate<ConfigDataEnvironmentContributor> filter, BinderOption... options) {
 		return getBinder(activationContext, filter, asBinderOptionsSet(options));
 	}
 
@@ -224,7 +225,7 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 				: EnumSet.copyOf(Arrays.asList(options));
 	}
 
-	private Binder getBinder(ConfigDataActivationContext activationContext,
+	private Binder getBinder(@Nullable ConfigDataActivationContext activationContext,
 			Predicate<ConfigDataEnvironmentContributor> filter, Set<BinderOption> options) {
 		boolean failOnInactiveSource = options.contains(BinderOption.FAIL_ON_BIND_TO_INACTIVE_SOURCE);
 		Iterable<ConfigurationPropertySource> sources = () -> getBinderSources(
@@ -279,12 +280,12 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 
 		private final ConfigDataEnvironmentContributor contributor;
 
-		private final ConfigDataActivationContext activationContext;
+		private final @Nullable ConfigDataActivationContext activationContext;
 
-		private volatile Binder binder;
+		private volatile @Nullable Binder binder;
 
 		ContributorConfigDataLocationResolverContext(ConfigDataEnvironmentContributors contributors,
-				ConfigDataEnvironmentContributor contributor, ConfigDataActivationContext activationContext) {
+				ConfigDataEnvironmentContributor contributor, @Nullable ConfigDataActivationContext activationContext) {
 			this.contributors = contributors;
 			this.contributor = contributor;
 			this.activationContext = activationContext;
@@ -301,7 +302,7 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 		}
 
 		@Override
-		public ConfigDataResource getParent() {
+		public @Nullable ConfigDataResource getParent() {
 			return this.contributor.getResource();
 		}
 
@@ -314,9 +315,9 @@ class ConfigDataEnvironmentContributors implements Iterable<ConfigDataEnvironmen
 
 	private class InactiveSourceChecker implements BindHandler {
 
-		private final ConfigDataActivationContext activationContext;
+		private final @Nullable ConfigDataActivationContext activationContext;
 
-		InactiveSourceChecker(ConfigDataActivationContext activationContext) {
+		InactiveSourceChecker(@Nullable ConfigDataActivationContext activationContext) {
 			this.activationContext = activationContext;
 		}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentPostProcessor.java

@@ -22,6 +22,7 @@ import java.util.Collections;
 import java.util.function.Supplier;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.ConfigurableBootstrapContext;
 import org.springframework.boot.DefaultBootstrapContext;
@@ -63,7 +64,7 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 
 	private final ConfigurableBootstrapContext bootstrapContext;
 
-	private final ConfigDataEnvironmentUpdateListener environmentUpdateListener;
+	private final @Nullable ConfigDataEnvironmentUpdateListener environmentUpdateListener;
 
 	public ConfigDataEnvironmentPostProcessor(DeferredLogFactory logFactory,
 			ConfigurableBootstrapContext bootstrapContext) {
@@ -72,7 +73,7 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 
 	private ConfigDataEnvironmentPostProcessor(DeferredLogFactory logFactory,
 			ConfigurableBootstrapContext bootstrapContext,
-			ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
+			@Nullable ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
 		this.logFactory = logFactory;
 		this.logger = logFactory.getLog(getClass());
 		this.bootstrapContext = bootstrapContext;
@@ -89,7 +90,7 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 		postProcessEnvironment(environment, application.getResourceLoader(), application.getAdditionalProfiles());
 	}
 
-	void postProcessEnvironment(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
+	void postProcessEnvironment(ConfigurableEnvironment environment, @Nullable ResourceLoader resourceLoader,
 			Collection<String> additionalProfiles) {
 		this.logger.trace("Post-processing environment to add config data");
 		resourceLoader = (resourceLoader != null) ? resourceLoader : new DefaultResourceLoader();
@@ -123,7 +124,7 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 	 * @param additionalProfiles any additional profiles that should be applied
 	 */
 	public static void applyTo(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
-			ConfigurableBootstrapContext bootstrapContext, String... additionalProfiles) {
+			@Nullable ConfigurableBootstrapContext bootstrapContext, String... additionalProfiles) {
 		applyTo(environment, resourceLoader, bootstrapContext, Arrays.asList(additionalProfiles));
 	}
 
@@ -137,8 +138,8 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 	 * throw-away context
 	 * @param additionalProfiles any additional profiles that should be applied
 	 */
-	public static void applyTo(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
-			ConfigurableBootstrapContext bootstrapContext, Collection<String> additionalProfiles) {
+	public static void applyTo(ConfigurableEnvironment environment, @Nullable ResourceLoader resourceLoader,
+			@Nullable ConfigurableBootstrapContext bootstrapContext, Collection<String> additionalProfiles) {
 		DeferredLogFactory logFactory = Supplier::get;
 		bootstrapContext = (bootstrapContext != null) ? bootstrapContext : new DefaultBootstrapContext();
 		ConfigDataEnvironmentPostProcessor postProcessor = new ConfigDataEnvironmentPostProcessor(logFactory,
@@ -160,7 +161,7 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 	 * {@link Environment} updates.
 	 */
 	public static void applyTo(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
-			ConfigurableBootstrapContext bootstrapContext, Collection<String> additionalProfiles,
+			@Nullable ConfigurableBootstrapContext bootstrapContext, Collection<String> additionalProfiles,
 			ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
 		DeferredLogFactory logFactory = Supplier::get;
 		bootstrapContext = (bootstrapContext != null) ? bootstrapContext : new DefaultBootstrapContext();

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentUpdateListener.java

@@ -18,6 +18,8 @@ package org.springframework.boot.context.config;
 
 import java.util.EventListener;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.config.ConfigData.Options;
 import org.springframework.core.env.Environment;
 import org.springframework.core.env.PropertySource;
@@ -43,8 +45,8 @@ public interface ConfigDataEnvironmentUpdateListener extends EventListener {
 	 * @param location the original {@link ConfigDataLocation} of the source.
 	 * @param resource the {@link ConfigDataResource} of the source.
 	 */
-	default void onPropertySourceAdded(PropertySource<?> propertySource, ConfigDataLocation location,
-			ConfigDataResource resource) {
+	default void onPropertySourceAdded(PropertySource<?> propertySource, @Nullable ConfigDataLocation location,
+			@Nullable ConfigDataResource resource) {
 	}
 
 	/**

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataException.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Abstract base class for configuration data exceptions.
  *
@@ -30,7 +32,7 @@ public abstract class ConfigDataException extends RuntimeException {
 	 * @param message the exception message
 	 * @param cause the exception cause
 	 */
-	protected ConfigDataException(String message, Throwable cause) {
+	protected ConfigDataException(String message, @Nullable Throwable cause) {
 		super(message, cause);
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataImporter.java

@@ -26,6 +26,7 @@ import java.util.Map;
 import java.util.Set;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.logging.DeferredLogFactory;
 import org.springframework.core.log.LogMessage;
@@ -78,7 +79,7 @@ class ConfigDataImporter {
 	 * @param locations the locations to resolve
 	 * @return a map of the loaded locations and data
 	 */
-	Map<ConfigDataResolutionResult, ConfigData> resolveAndLoad(ConfigDataActivationContext activationContext,
+	Map<ConfigDataResolutionResult, ConfigData> resolveAndLoad(@Nullable ConfigDataActivationContext activationContext,
 			ConfigDataLocationResolverContext locationResolverContext, ConfigDataLoaderContext loaderContext,
 			List<ConfigDataLocation> locations) {
 		try {
@@ -92,7 +93,7 @@ class ConfigDataImporter {
 	}
 
 	private List<ConfigDataResolutionResult> resolve(ConfigDataLocationResolverContext locationResolverContext,
-			Profiles profiles, List<ConfigDataLocation> locations) {
+			@Nullable Profiles profiles, List<ConfigDataLocation> locations) {
 		List<ConfigDataResolutionResult> resolved = new ArrayList<>(locations.size());
 		for (ConfigDataLocation location : locations) {
 			resolved.addAll(resolve(locationResolverContext, profiles, location));
@@ -101,7 +102,7 @@ class ConfigDataImporter {
 	}
 
 	private List<ConfigDataResolutionResult> resolve(ConfigDataLocationResolverContext locationResolverContext,
-			Profiles profiles, ConfigDataLocation location) {
+			@Nullable Profiles profiles, ConfigDataLocation location) {
 		try {
 			return this.resolvers.resolve(locationResolverContext, location, profiles);
 		}
@@ -145,14 +146,16 @@ class ConfigDataImporter {
 		return Collections.unmodifiableMap(result);
 	}
 
-	private void handle(ConfigDataNotFoundException ex, ConfigDataLocation location, ConfigDataResource resource) {
+	private void handle(ConfigDataNotFoundException ex, ConfigDataLocation location,
+			@Nullable ConfigDataResource resource) {
 		if (ex instanceof ConfigDataResourceNotFoundException notFoundException) {
 			ex = notFoundException.withLocation(location);
 		}
 		getNotFoundAction(location, resource).handle(this.logger, ex);
 	}
 
-	private ConfigDataNotFoundAction getNotFoundAction(ConfigDataLocation location, ConfigDataResource resource) {
+	private ConfigDataNotFoundAction getNotFoundAction(ConfigDataLocation location,
+			@Nullable ConfigDataResource resource) {
 		if (location.isOptional() || (resource != null && resource.isOptional())) {
 			return ConfigDataNotFoundAction.IGNORE;
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLoader.java

@@ -18,6 +18,8 @@ package org.springframework.boot.context.config;
 
 import java.io.IOException;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.BootstrapContext;
 import org.springframework.boot.BootstrapRegistry;
 import org.springframework.boot.ConfigurableBootstrapContext;
@@ -61,7 +63,7 @@ public interface ConfigDataLoader<R extends ConfigDataResource> {
 	 * @throws IOException on IO error
 	 * @throws ConfigDataResourceNotFoundException if the resource cannot be found
 	 */
-	ConfigData load(ConfigDataLoaderContext context, R resource)
+	@Nullable ConfigData load(ConfigDataLoaderContext context, R resource)
 			throws IOException, ConfigDataResourceNotFoundException;
 
 }

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLoaders.java

@@ -22,6 +22,7 @@ import java.util.Collections;
 import java.util.List;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.BootstrapContext;
 import org.springframework.boot.BootstrapRegistry;
@@ -78,7 +79,7 @@ class ConfigDataLoaders {
 		return Collections.unmodifiableList(resourceTypes);
 	}
 
-	private Class<?> getResourceType(ConfigDataLoader<?> loader) {
+	private @Nullable Class<?> getResourceType(ConfigDataLoader<?> loader) {
 		return ResolvableType.forClass(loader.getClass()).as(ConfigDataLoader.class).resolveGeneric();
 	}
 
@@ -90,7 +91,8 @@ class ConfigDataLoaders {
 	 * @return the loaded {@link ConfigData}
 	 * @throws IOException on IO error
 	 */
-	<R extends ConfigDataResource> ConfigData load(ConfigDataLoaderContext context, R resource) throws IOException {
+	<R extends ConfigDataResource> @Nullable ConfigData load(ConfigDataLoaderContext context, R resource)
+			throws IOException {
 		ConfigDataLoader<R> loader = getLoader(context, resource);
 		this.logger.trace(LogMessage.of(() -> "Loading " + resource + " using loader " + loader.getClass().getName()));
 		return loader.load(context, resource);

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLocation.java

@@ -16,8 +16,11 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.origin.Origin;
 import org.springframework.boot.origin.OriginProvider;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -44,9 +47,9 @@ public final class ConfigDataLocation implements OriginProvider {
 
 	private final String value;
 
-	private final Origin origin;
+	private final @Nullable Origin origin;
 
-	private ConfigDataLocation(boolean optional, String value, Origin origin) {
+	private ConfigDataLocation(boolean optional, String value, @Nullable Origin origin) {
 		this.value = value;
 		this.optional = optional;
 		this.origin = origin;
@@ -93,7 +96,7 @@ public final class ConfigDataLocation implements OriginProvider {
 	}
 
 	@Override
-	public Origin getOrigin() {
+	public @Nullable Origin getOrigin() {
 		return this.origin;
 	}
 
@@ -118,7 +121,10 @@ public final class ConfigDataLocation implements OriginProvider {
 		String[] values = StringUtils.delimitedListToStringArray(toString(), delimiter);
 		ConfigDataLocation[] result = new ConfigDataLocation[values.length];
 		for (int i = 0; i < values.length; i++) {
-			result[i] = of(values[i]).withOrigin(getOrigin());
+			int index = i;
+			ConfigDataLocation configDataLocation = of(values[index]);
+			Assert.state(configDataLocation != null, () -> "Unable to parse '%s'".formatted(values[index]));
+			result[i] = configDataLocation.withOrigin(getOrigin());
 		}
 		return result;
 	}
@@ -150,7 +156,7 @@ public final class ConfigDataLocation implements OriginProvider {
 	 * @param origin the origin to set
 	 * @return a new {@link ConfigDataLocation} instance.
 	 */
-	ConfigDataLocation withOrigin(Origin origin) {
+	ConfigDataLocation withOrigin(@Nullable Origin origin) {
 		return new ConfigDataLocation(this.optional, this.value, origin);
 	}
 
@@ -160,9 +166,16 @@ public final class ConfigDataLocation implements OriginProvider {
 	 * @return a {@link ConfigDataLocation} instance or {@code null} if no location was
 	 * provided
 	 */
-	public static ConfigDataLocation of(String location) {
+	public static @Nullable ConfigDataLocation of(@Nullable String location) {
 		boolean optional = location != null && location.startsWith(OPTIONAL_PREFIX);
-		String value = (!optional) ? location : location.substring(OPTIONAL_PREFIX.length());
+		String value;
+		if (optional) {
+			Assert.state(location != null, "'location' can't be null here");
+			value = location.substring(OPTIONAL_PREFIX.length());
+		}
+		else {
+			value = location;
+		}
 		if (!StringUtils.hasText(value)) {
 			return null;
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLocationNotFoundException.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.origin.Origin;
 import org.springframework.util.Assert;
 
@@ -43,7 +45,7 @@ public class ConfigDataLocationNotFoundException extends ConfigDataNotFoundExcep
 	 * @param location the location that could not be found
 	 * @param cause the exception cause
 	 */
-	public ConfigDataLocationNotFoundException(ConfigDataLocation location, Throwable cause) {
+	public ConfigDataLocationNotFoundException(ConfigDataLocation location, @Nullable Throwable cause) {
 		this(location, getMessage(location), cause);
 	}
 
@@ -54,7 +56,7 @@ public class ConfigDataLocationNotFoundException extends ConfigDataNotFoundExcep
 	 * @param cause the exception cause
 	 * @since 2.4.7
 	 */
-	public ConfigDataLocationNotFoundException(ConfigDataLocation location, String message, Throwable cause) {
+	public ConfigDataLocationNotFoundException(ConfigDataLocation location, String message, @Nullable Throwable cause) {
 		super(message, cause);
 		Assert.notNull(location, "'location' must not be null");
 		this.location = location;
@@ -69,7 +71,7 @@ public class ConfigDataLocationNotFoundException extends ConfigDataNotFoundExcep
 	}
 
 	@Override
-	public Origin getOrigin() {
+	public @Nullable Origin getOrigin() {
 		return Origin.from(this.location);
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLocationResolverContext.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.ConfigurableBootstrapContext;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.env.EnvironmentPostProcessor;
@@ -41,7 +43,7 @@ public interface ConfigDataLocationResolverContext {
 	 * or {@code null} if there is no available parent.
 	 * @return the parent location
 	 */
-	ConfigDataResource getParent();
+	@Nullable ConfigDataResource getParent();
 
 	/**
 	 * Provides access to the {@link ConfigurableBootstrapContext} shared across all

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLocationResolvers.java

@@ -22,6 +22,7 @@ import java.util.List;
 import java.util.function.Supplier;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.BootstrapContext;
 import org.springframework.boot.BootstrapRegistry;
@@ -84,8 +85,8 @@ class ConfigDataLocationResolvers {
 		return Collections.unmodifiableList(reordered);
 	}
 
-	List<ConfigDataResolutionResult> resolve(ConfigDataLocationResolverContext context, ConfigDataLocation location,
-			Profiles profiles) {
+	List<ConfigDataResolutionResult> resolve(ConfigDataLocationResolverContext context,
+			@Nullable ConfigDataLocation location, @Nullable Profiles profiles) {
 		if (location == null) {
 			return Collections.emptyList();
 		}
@@ -98,7 +99,7 @@ class ConfigDataLocationResolvers {
 	}
 
 	private List<ConfigDataResolutionResult> resolve(ConfigDataLocationResolver<?> resolver,
-			ConfigDataLocationResolverContext context, ConfigDataLocation location, Profiles profiles) {
+			ConfigDataLocationResolverContext context, ConfigDataLocation location, @Nullable Profiles profiles) {
 		List<ConfigDataResolutionResult> resolved = resolve(location, false, () -> resolver.resolve(context, location));
 		if (profiles == null) {
 			return resolved;
@@ -119,7 +120,7 @@ class ConfigDataLocationResolvers {
 	}
 
 	@SuppressWarnings("unchecked")
-	private <T> List<T> nonNullList(List<? extends T> list) {
+	private <T> List<T> nonNullList(@Nullable List<? extends T> list) {
 		return (list != null) ? (List<T>) list : Collections.emptyList();
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLocationRuntimeHints.java

@@ -22,6 +22,7 @@ import java.util.List;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
@@ -41,7 +42,7 @@ class ConfigDataLocationRuntimeHints implements RuntimeHintsRegistrar {
 	private static final Log logger = LogFactory.getLog(ConfigDataLocationRuntimeHints.class);
 
 	@Override
-	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+	public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 		List<String> fileNames = getFileNames(classLoader);
 		List<String> locations = getLocations(classLoader);
 		List<String> extensions = getExtensions(classLoader);
@@ -60,7 +61,7 @@ class ConfigDataLocationRuntimeHints implements RuntimeHintsRegistrar {
 	 * @param classLoader the classloader to use
 	 * @return the configuration file names
 	 */
-	protected List<String> getFileNames(ClassLoader classLoader) {
+	protected List<String> getFileNames(@Nullable ClassLoader classLoader) {
 		return Arrays.asList(StandardConfigDataLocationResolver.DEFAULT_CONFIG_NAMES);
 	}
 
@@ -70,7 +71,7 @@ class ConfigDataLocationRuntimeHints implements RuntimeHintsRegistrar {
 	 * @param classLoader the classloader to use
 	 * @return the configuration file locations
 	 */
-	protected List<String> getLocations(ClassLoader classLoader) {
+	protected List<String> getLocations(@Nullable ClassLoader classLoader) {
 		List<String> classpathLocations = new ArrayList<>();
 		for (ConfigDataLocation candidate : ConfigDataEnvironment.DEFAULT_SEARCH_LOCATIONS) {
 			for (ConfigDataLocation configDataLocation : candidate.split()) {
@@ -89,7 +90,7 @@ class ConfigDataLocationRuntimeHints implements RuntimeHintsRegistrar {
 	 * @param classLoader the classloader to use
 	 * @return the configuration file extensions
 	 */
-	protected List<String> getExtensions(ClassLoader classLoader) {
+	protected List<String> getExtensions(@Nullable ClassLoader classLoader) {
 		List<String> extensions = new ArrayList<>();
 		List<PropertySourceLoader> propertySourceLoaders = getSpringFactoriesLoader(classLoader)
 			.load(PropertySourceLoader.class);
@@ -104,7 +105,7 @@ class ConfigDataLocationRuntimeHints implements RuntimeHintsRegistrar {
 		return extensions;
 	}
 
-	protected SpringFactoriesLoader getSpringFactoriesLoader(ClassLoader classLoader) {
+	protected SpringFactoriesLoader getSpringFactoriesLoader(@Nullable ClassLoader classLoader) {
 		return SpringFactoriesLoader.forDefaultResourceLocation(classLoader);
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataNotFoundException.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.origin.OriginProvider;
 
 /**
@@ -31,7 +33,7 @@ public abstract class ConfigDataNotFoundException extends ConfigDataException im
 	 * @param message the exception message
 	 * @param cause the exception cause
 	 */
-	ConfigDataNotFoundException(String message, Throwable cause) {
+	ConfigDataNotFoundException(String message, @Nullable Throwable cause) {
 		super(message, cause);
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataNotFoundFailureAnalyzer.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
 import org.springframework.boot.diagnostics.FailureAnalysis;
 import org.springframework.boot.origin.Origin;
@@ -48,7 +50,7 @@ class ConfigDataNotFoundFailureAnalyzer extends AbstractFailureAnalyzer<ConfigDa
 		return new FailureAnalysis(message, action.toString(), cause);
 	}
 
-	private ConfigDataLocation getLocation(ConfigDataNotFoundException cause) {
+	private @Nullable ConfigDataLocation getLocation(ConfigDataNotFoundException cause) {
 		if (cause instanceof ConfigDataLocationNotFoundException locationNotFoundException) {
 			return locationNotFoundException.getLocation();
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataProperties.java

@@ -20,6 +20,8 @@ import java.util.Collections;
 import java.util.List;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.cloud.CloudPlatform;
 import org.springframework.boot.context.properties.bind.Bindable;
 import org.springframework.boot.context.properties.bind.Binder;
@@ -42,14 +44,14 @@ class ConfigDataProperties {
 
 	private final List<ConfigDataLocation> imports;
 
-	private final Activate activate;
+	private final @Nullable Activate activate;
 
 	/**
 	 * Create a new {@link ConfigDataProperties} instance.
 	 * @param imports the imports requested
 	 * @param activate the activate properties
 	 */
-	ConfigDataProperties(@Name("import") List<ConfigDataLocation> imports, Activate activate) {
+	ConfigDataProperties(@Nullable @Name("import") List<ConfigDataLocation> imports, @Nullable Activate activate) {
 		this.imports = (imports != null) ? imports : Collections.emptyList();
 		this.activate = activate;
 	}
@@ -68,7 +70,7 @@ class ConfigDataProperties {
 	 * @param activationContext the activation context
 	 * @return {@code true} if the config data property source is active
 	 */
-	boolean isActive(ConfigDataActivationContext activationContext) {
+	boolean isActive(@Nullable ConfigDataActivationContext activationContext) {
 		return this.activate == null || this.activate.isActive(activationContext);
 	}
 
@@ -86,7 +88,7 @@ class ConfigDataProperties {
 	 * @param binder the binder used to bind the properties
 	 * @return a {@link ConfigDataProperties} instance or {@code null}
 	 */
-	static ConfigDataProperties get(Binder binder) {
+	static @Nullable ConfigDataProperties get(Binder binder) {
 		return binder.bind(NAME, BINDABLE_PROPERTIES, new ConfigDataLocationBindHandler()).orElse(null);
 	}
 
@@ -95,7 +97,7 @@ class ConfigDataProperties {
 	 */
 	static class Activate {
 
-		private final CloudPlatform onCloudPlatform;
+		private final @Nullable CloudPlatform onCloudPlatform;
 
 		private final String[] onProfile;
 
@@ -104,7 +106,7 @@ class ConfigDataProperties {
 		 * @param onCloudPlatform the cloud platform required for activation
 		 * @param onProfile the profile expression required for activation
 		 */
-		Activate(CloudPlatform onCloudPlatform, String[] onProfile) {
+		Activate(@Nullable CloudPlatform onCloudPlatform, String[] onProfile) {
 			this.onProfile = onProfile;
 			this.onCloudPlatform = onCloudPlatform;
 		}
@@ -115,7 +117,7 @@ class ConfigDataProperties {
 		 * @param activationContext the activation context
 		 * @return {@code true} if the config data property source is active
 		 */
-		boolean isActive(ConfigDataActivationContext activationContext) {
+		boolean isActive(@Nullable ConfigDataActivationContext activationContext) {
 			if (activationContext == null) {
 				return false;
 			}
@@ -129,7 +131,7 @@ class ConfigDataProperties {
 			return this.onCloudPlatform == null || this.onCloudPlatform == cloudPlatform;
 		}
 
-		private boolean isActive(Profiles profiles) {
+		private boolean isActive(@Nullable Profiles profiles) {
 			return ObjectUtils.isEmpty(this.onProfile)
 					|| (profiles != null && matchesActiveProfiles(profiles::isAccepted));
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataPropertiesRuntimeHints.java

@@ -16,10 +16,15 @@
 
 package org.springframework.boot.context.config;
 
+import java.lang.reflect.Method;
+
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.ExecutableMode;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.boot.context.properties.bind.BindableRuntimeHintsRegistrar;
+import org.springframework.util.Assert;
 import org.springframework.util.ReflectionUtils;
 
 /**
@@ -30,11 +35,11 @@ import org.springframework.util.ReflectionUtils;
 class ConfigDataPropertiesRuntimeHints implements RuntimeHintsRegistrar {
 
 	@Override
-	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+	public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 		BindableRuntimeHintsRegistrar.forTypes(ConfigDataProperties.class).registerHints(hints);
-		hints.reflection()
-			.registerMethod(ReflectionUtils.findMethod(ConfigDataLocation.class, "of", String.class),
-					ExecutableMode.INVOKE);
+		Method method = ReflectionUtils.findMethod(ConfigDataLocation.class, "of", String.class);
+		Assert.state(method != null, "'method' must not be null");
+		hints.reflection().registerMethod(method, ExecutableMode.INVOKE);
 	}
 
 }

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataResourceNotFoundException.java

@@ -20,6 +20,8 @@ import java.io.File;
 import java.nio.file.Files;
 import java.nio.file.Path;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.origin.Origin;
 import org.springframework.core.io.Resource;
 import org.springframework.util.Assert;
@@ -35,7 +37,7 @@ public class ConfigDataResourceNotFoundException extends ConfigDataNotFoundExcep
 
 	private final ConfigDataResource resource;
 
-	private final ConfigDataLocation location;
+	private final @Nullable ConfigDataLocation location;
 
 	/**
 	 * Create a new {@link ConfigDataResourceNotFoundException} instance.
@@ -50,12 +52,12 @@ public class ConfigDataResourceNotFoundException extends ConfigDataNotFoundExcep
 	 * @param resource the resource that could not be found
 	 * @param cause the exception cause
 	 */
-	public ConfigDataResourceNotFoundException(ConfigDataResource resource, Throwable cause) {
+	public ConfigDataResourceNotFoundException(ConfigDataResource resource, @Nullable Throwable cause) {
 		this(resource, null, cause);
 	}
 
-	private ConfigDataResourceNotFoundException(ConfigDataResource resource, ConfigDataLocation location,
-			Throwable cause) {
+	private ConfigDataResourceNotFoundException(ConfigDataResource resource, @Nullable ConfigDataLocation location,
+			@Nullable Throwable cause) {
 		super(getMessage(resource, location), cause);
 		Assert.notNull(resource, "'resource' must not be null");
 		this.resource = resource;
@@ -74,12 +76,12 @@ public class ConfigDataResourceNotFoundException extends ConfigDataNotFoundExcep
 	 * Return the original location that was resolved to determine the resource.
 	 * @return the location or {@code null} if no location is available
 	 */
-	public ConfigDataLocation getLocation() {
+	public @Nullable ConfigDataLocation getLocation() {
 		return this.location;
 	}
 
 	@Override
-	public Origin getOrigin() {
+	public @Nullable Origin getOrigin() {
 		return Origin.from(this.location);
 	}
 
@@ -97,11 +99,11 @@ public class ConfigDataResourceNotFoundException extends ConfigDataNotFoundExcep
 		return new ConfigDataResourceNotFoundException(this.resource, location, getCause());
 	}
 
-	private static String getMessage(ConfigDataResource resource, ConfigDataLocation location) {
+	private static String getMessage(ConfigDataResource resource, @Nullable ConfigDataLocation location) {
 		return String.format("Config data %s cannot be found", getReferenceDescription(resource, location));
 	}
 
-	private static String getReferenceDescription(ConfigDataResource resource, ConfigDataLocation location) {
+	private static String getReferenceDescription(ConfigDataResource resource, @Nullable ConfigDataLocation location) {
 		String description = String.format("resource '%s'", resource);
 		if (location != null) {
 			description += String.format(" via location '%s'", location);

core/spring-boot/src/main/java/org/springframework/boot/context/config/FileExtensionHint.java

@@ -19,6 +19,8 @@ package org.springframework.boot.context.config;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * User-provided hint for an otherwise missing file extension.
  *
@@ -30,9 +32,9 @@ final class FileExtensionHint {
 
 	private static final FileExtensionHint NONE = new FileExtensionHint(null);
 
-	private final Matcher matcher;
+	private final @Nullable Matcher matcher;
 
-	private FileExtensionHint(Matcher matcher) {
+	private FileExtensionHint(@Nullable Matcher matcher) {
 		this.matcher = matcher;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/InactiveConfigDataAccessException.java

@@ -16,11 +16,14 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.source.ConfigurationProperty;
 import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
 import org.springframework.boot.origin.Origin;
 import org.springframework.core.env.PropertySource;
+import org.springframework.util.Assert;
 
 /**
  * Exception thrown when an attempt is made to resolve a property against an inactive
@@ -35,11 +38,11 @@ public class InactiveConfigDataAccessException extends ConfigDataException {
 
 	private final PropertySource<?> propertySource;
 
-	private final ConfigDataResource location;
+	private final @Nullable ConfigDataResource location;
 
 	private final String propertyName;
 
-	private final Origin origin;
+	private final @Nullable Origin origin;
 
 	/**
 	 * Create a new {@link InactiveConfigDataAccessException} instance.
@@ -49,8 +52,8 @@ public class InactiveConfigDataAccessException extends ConfigDataException {
 	 * @param propertyName the name of the property
 	 * @param origin the origin or the property or {@code null}
 	 */
-	InactiveConfigDataAccessException(PropertySource<?> propertySource, ConfigDataResource location,
-			String propertyName, Origin origin) {
+	InactiveConfigDataAccessException(PropertySource<?> propertySource, @Nullable ConfigDataResource location,
+			String propertyName, @Nullable Origin origin) {
 		super(getMessage(propertySource, location, propertyName, origin), null);
 		this.propertySource = propertySource;
 		this.location = location;
@@ -58,8 +61,8 @@ public class InactiveConfigDataAccessException extends ConfigDataException {
 		this.origin = origin;
 	}
 
-	private static String getMessage(PropertySource<?> propertySource, ConfigDataResource location, String propertyName,
-			Origin origin) {
+	private static String getMessage(PropertySource<?> propertySource, @Nullable ConfigDataResource location,
+			String propertyName, @Nullable Origin origin) {
 		StringBuilder message = new StringBuilder("Inactive property source '");
 		message.append(propertySource.getName());
 		if (location != null) {
@@ -90,7 +93,7 @@ public class InactiveConfigDataAccessException extends ConfigDataException {
 	 * source was not loaded from {@link ConfigData}.
 	 * @return the config data location or {@code null}
 	 */
-	public ConfigDataResource getLocation() {
+	public @Nullable ConfigDataResource getLocation() {
 		return this.location;
 	}
 
@@ -106,7 +109,7 @@ public class InactiveConfigDataAccessException extends ConfigDataException {
 	 * Return the origin or the property or {@code null}.
 	 * @return the property origin
 	 */
-	public Origin getOrigin() {
+	public @Nullable Origin getOrigin() {
 		return this.origin;
 	}
 
@@ -122,6 +125,7 @@ public class InactiveConfigDataAccessException extends ConfigDataException {
 		if (property != null) {
 			PropertySource<?> propertySource = contributor.getPropertySource();
 			ConfigDataResource location = contributor.getResource();
+			Assert.state(propertySource != null, "'propertySource' must not be null");
 			throw new InactiveConfigDataAccessException(propertySource, location, name.toString(),
 					property.getOrigin());
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/config/InvalidConfigDataPropertyException.java

@@ -22,6 +22,8 @@ import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.source.ConfigurationProperty;
 import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
@@ -60,12 +62,12 @@ public class InvalidConfigDataPropertyException extends ConfigDataException {
 
 	private final ConfigurationProperty property;
 
-	private final ConfigurationPropertyName replacement;
+	private final @Nullable ConfigurationPropertyName replacement;
 
-	private final ConfigDataResource location;
+	private final @Nullable ConfigDataResource location;
 
 	InvalidConfigDataPropertyException(ConfigurationProperty property, boolean profileSpecific,
-			ConfigurationPropertyName replacement, ConfigDataResource location) {
+			@Nullable ConfigurationPropertyName replacement, @Nullable ConfigDataResource location) {
 		super(getMessage(property, profileSpecific, replacement, location), null);
 		this.property = property;
 		this.replacement = replacement;
@@ -85,7 +87,7 @@ public class InvalidConfigDataPropertyException extends ConfigDataException {
 	 * the source was not loaded from {@link ConfigData}.
 	 * @return the config data location or {@code null}
 	 */
-	public ConfigDataResource getLocation() {
+	public @Nullable ConfigDataResource getLocation() {
 		return this.location;
 	}
 
@@ -94,7 +96,7 @@ public class InvalidConfigDataPropertyException extends ConfigDataException {
 	 * replacement is available.
 	 * @return the replacement property name
 	 */
-	public ConfigurationPropertyName getReplacement() {
+	public @Nullable ConfigurationPropertyName getReplacement() {
 		return this.replacement;
 	}
 
@@ -126,7 +128,7 @@ public class InvalidConfigDataPropertyException extends ConfigDataException {
 	}
 
 	private static String getMessage(ConfigurationProperty property, boolean profileSpecific,
-			ConfigurationPropertyName replacement, ConfigDataResource location) {
+			@Nullable ConfigurationPropertyName replacement, @Nullable ConfigDataResource location) {
 		StringBuilder message = new StringBuilder("Property '");
 		message.append(property.getName());
 		if (location != null) {

core/spring-boot/src/main/java/org/springframework/boot/context/config/Profiles.java

@@ -28,6 +28,8 @@ import java.util.List;
 import java.util.Set;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.bind.BindResult;
 import org.springframework.boot.context.properties.bind.Bindable;
 import org.springframework.boot.context.properties.bind.Binder;
@@ -77,7 +79,7 @@ public class Profiles implements Iterable<String> {
 	 * @param binder the binder for profile properties
 	 * @param additionalProfiles any additional active profiles
 	 */
-	Profiles(Environment environment, Binder binder, Collection<String> additionalProfiles) {
+	Profiles(Environment environment, Binder binder, @Nullable Collection<String> additionalProfiles) {
 		ProfilesValidator validator = ProfilesValidator.get(binder);
 		if (additionalProfiles != null) {
 			validator.validate(additionalProfiles, () -> "Invalid profile property value found in additional profiles");
@@ -89,7 +91,7 @@ public class Profiles implements Iterable<String> {
 	}
 
 	private List<String> getActivatedProfiles(Environment environment, Binder binder, ProfilesValidator validator,
-			Collection<String> additionalProfiles) {
+			@Nullable Collection<String> additionalProfiles) {
 		return asUniqueItemList(getProfiles(environment, binder, validator, Type.ACTIVE), additionalProfiles);
 	}
 
@@ -117,7 +119,7 @@ public class Profiles implements Iterable<String> {
 		return boundProfiles.orElse(type.getDefaultValue());
 	}
 
-	private boolean hasProgrammaticallySetProfiles(Type type, String environmentPropertyValue,
+	private boolean hasProgrammaticallySetProfiles(Type type, @Nullable String environmentPropertyValue,
 			Set<String> environmentPropertyProfiles, Set<String> environmentProfiles) {
 		if (!StringUtils.hasLength(environmentPropertyValue)) {
 			return !type.getDefaultValue().equals(environmentProfiles);
@@ -134,7 +136,7 @@ public class Profiles implements Iterable<String> {
 		return result;
 	}
 
-	private List<String> expandProfiles(List<String> profiles) {
+	private List<String> expandProfiles(@Nullable List<String> profiles) {
 		Deque<String> stack = new ArrayDeque<>();
 		asReversedList(profiles).forEach(stack::push);
 		Set<String> expandedProfiles = new LinkedHashSet<>();
@@ -147,7 +149,7 @@ public class Profiles implements Iterable<String> {
 		return asUniqueItemList(expandedProfiles);
 	}
 
-	private List<String> asReversedList(List<String> list) {
+	private List<String> asReversedList(@Nullable List<String> list) {
 		if (CollectionUtils.isEmpty(list)) {
 			return Collections.emptyList();
 		}
@@ -160,7 +162,7 @@ public class Profiles implements Iterable<String> {
 		return asUniqueItemList(profiles, null);
 	}
 
-	private List<String> asUniqueItemList(Collection<String> profiles, Collection<String> additional) {
+	private List<String> asUniqueItemList(Collection<String> profiles, @Nullable Collection<String> additional) {
 		LinkedHashSet<String> uniqueItems = new LinkedHashSet<>();
 		if (!CollectionUtils.isEmpty(additional)) {
 			uniqueItems.addAll(additional);

core/spring-boot/src/main/java/org/springframework/boot/context/config/ProfilesValidator.java

@@ -22,6 +22,8 @@ import java.util.Map;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.bind.BindContext;
 import org.springframework.boot.context.properties.bind.BindHandler;
 import org.springframework.boot.context.properties.bind.Bindable;
@@ -61,7 +63,7 @@ final class ProfilesValidator implements BindHandler {
 		}
 	}
 
-	private void validate(Object value) {
+	private void validate(@Nullable Object value) {
 		if (!this.validate) {
 			return;
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/config/StandardConfigDataLocationResolver.java

@@ -30,6 +30,7 @@ import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.context.config.LocationResourceLoader.ResourceType;
 import org.springframework.boot.context.properties.bind.Binder;
@@ -67,7 +68,7 @@ public class StandardConfigDataLocationResolver
 
 	private static final Pattern URL_PREFIX = Pattern.compile("^([a-zA-Z][a-zA-Z0-9*]*?:)(.*$)");
 
-	private static final String NO_PROFILE = null;
+	private static final @Nullable String NO_PROFILE = null;
 
 	private final Log logger;
 
@@ -186,7 +187,7 @@ public class StandardConfigDataLocationResolver
 	}
 
 	private Set<StandardConfigDataReference> getReferencesForDirectory(ConfigDataLocation configDataLocation,
-			String directory, String profile) {
+			String directory, @Nullable String profile) {
 		Set<StandardConfigDataReference> references = new LinkedHashSet<>();
 		for (String name : this.configNames) {
 			Deque<StandardConfigDataReference> referencesForName = getReferencesForConfigName(name, configDataLocation,
@@ -197,7 +198,7 @@ public class StandardConfigDataLocationResolver
 	}
 
 	private Deque<StandardConfigDataReference> getReferencesForConfigName(String name,
-			ConfigDataLocation configDataLocation, String directory, String profile) {
+			ConfigDataLocation configDataLocation, String directory, @Nullable String profile) {
 		Deque<StandardConfigDataReference> references = new ArrayDeque<>();
 		for (PropertySourceLoader propertySourceLoader : this.propertySourceLoaders) {
 			for (String extension : propertySourceLoader.getFileExtensions()) {
@@ -212,7 +213,7 @@ public class StandardConfigDataLocationResolver
 	}
 
 	private Set<StandardConfigDataReference> getReferencesForFile(ConfigDataLocation configDataLocation, String file,
-			String profile) {
+			@Nullable String profile) {
 		FileExtensionHint fileExtensionHint = FileExtensionHint.from(file);
 		if (fileExtensionHint.isPresent()) {
 			file = FileExtensionHint.removeFrom(file) + fileExtensionHint;
@@ -242,7 +243,7 @@ public class StandardConfigDataLocationResolver
 						+ "check the location prefix if a different resolver is expected");
 	}
 
-	private String getLoadableFileExtension(PropertySourceLoader loader, String file) {
+	private @Nullable String getLoadableFileExtension(PropertySourceLoader loader, String file) {
 		for (String fileExtension : loader.getFileExtensions()) {
 			if (StringUtils.endsWithIgnoreCase(file, fileExtension)) {
 				return fileExtension;
@@ -285,13 +286,17 @@ public class StandardConfigDataLocationResolver
 	}
 
 	private Set<StandardConfigDataResource> resolveNonPatternEmptyDirectories(StandardConfigDataReference reference) {
-		Resource resource = this.resourceLoader.getResource(reference.getDirectory());
+		String directory = reference.getDirectory();
+		Assert.state(directory != null, "'directory' must not be null");
+		Resource resource = this.resourceLoader.getResource(directory);
 		return (resource instanceof ClassPathResource || !resource.exists()) ? Collections.emptySet()
 				: Collections.singleton(new StandardConfigDataResource(reference, resource, true));
 	}
 
 	private Set<StandardConfigDataResource> resolvePatternEmptyDirectories(StandardConfigDataReference reference) {
-		Resource[] subdirectories = this.resourceLoader.getResources(reference.getDirectory(), ResourceType.DIRECTORY);
+		String directory = reference.getDirectory();
+		Assert.state(directory != null, "'directory' must not be null");
+		Resource[] subdirectories = this.resourceLoader.getResources(directory, ResourceType.DIRECTORY);
 		ConfigDataLocation location = reference.getConfigDataLocation();
 		if (!location.isOptional() && ObjectUtils.isEmpty(subdirectories)) {
 			String message = String.format("Config data location '%s' contains no subdirectories", location);

core/spring-boot/src/main/java/org/springframework/boot/context/config/StandardConfigDataReference.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.config;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.env.PropertySourceLoader;
 import org.springframework.util.StringUtils;
 
@@ -31,9 +33,9 @@ class StandardConfigDataReference {
 
 	private final String resourceLocation;
 
-	private final String directory;
+	private final @Nullable String directory;
 
-	private final String profile;
+	private final @Nullable String profile;
 
 	private final PropertySourceLoader propertySourceLoader;
 
@@ -48,8 +50,8 @@ class StandardConfigDataReference {
 	 * @param propertySourceLoader the property source loader that should be used for this
 	 * reference
 	 */
-	StandardConfigDataReference(ConfigDataLocation configDataLocation, String directory, String root, String profile,
-			String extension, PropertySourceLoader propertySourceLoader) {
+	StandardConfigDataReference(ConfigDataLocation configDataLocation, @Nullable String directory, String root,
+			@Nullable String profile, @Nullable String extension, PropertySourceLoader propertySourceLoader) {
 		this.configDataLocation = configDataLocation;
 		String profileSuffix = (StringUtils.hasText(profile)) ? "-" + profile : "";
 		this.resourceLocation = root + profileSuffix + ((extension != null) ? "." + extension : "");
@@ -70,11 +72,11 @@ class StandardConfigDataReference {
 		return !this.configDataLocation.isOptional() && this.directory != null;
 	}
 
-	String getDirectory() {
+	@Nullable String getDirectory() {
 		return this.directory;
 	}
 
-	String getProfile() {
+	@Nullable String getProfile() {
 		return this.profile;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/config/StandardConfigDataResource.java

@@ -19,6 +19,8 @@ package org.springframework.boot.context.config;
 import java.io.File;
 import java.io.IOException;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.FileUrlResource;
@@ -81,7 +83,7 @@ public class StandardConfigDataResource extends ConfigDataResource {
 	 * @return the profile or {@code null}
 	 * @since 2.4.6
 	 */
-	public String getProfile() {
+	public @Nullable String getProfile() {
 		return this.reference.getProfile();
 	}
 
@@ -105,7 +107,7 @@ public class StandardConfigDataResource extends ConfigDataResource {
 		return ours.equals(other) || isSameFile(getUnderlyingFile(ours), getUnderlyingFile(other));
 	}
 
-	private boolean isSameFile(File ours, File other) {
+	private boolean isSameFile(@Nullable File ours, @Nullable File other) {
 		return (ours != null) && ours.equals(other);
 	}
 
@@ -128,7 +130,7 @@ public class StandardConfigDataResource extends ConfigDataResource {
 		return this.resource.toString();
 	}
 
-	private File getUnderlyingFile(Resource resource) {
+	private @Nullable File getUnderlyingFile(Resource resource) {
 		try {
 			if (resource instanceof ClassPathResource || resource instanceof FileSystemResource
 					|| resource instanceof FileUrlResource) {

core/spring-boot/src/main/java/org/springframework/boot/context/config/SystemEnvironmentConfigDataLocationResolver.java

@@ -20,6 +20,8 @@ import java.util.Collections;
 import java.util.List;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.env.PropertySourceLoader;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 
@@ -38,7 +40,7 @@ class SystemEnvironmentConfigDataLocationResolver
 
 	private final List<PropertySourceLoader> loaders;
 
-	private final Function<String, String> environment;
+	private final Function<String, @Nullable String> environment;
 
 	SystemEnvironmentConfigDataLocationResolver() {
 		this.loaders = SpringFactoriesLoader.loadFactories(PropertySourceLoader.class, getClass().getClassLoader());
@@ -46,7 +48,7 @@ class SystemEnvironmentConfigDataLocationResolver
 	}
 
 	SystemEnvironmentConfigDataLocationResolver(List<PropertySourceLoader> loaders,
-			Function<String, String> environment) {
+			Function<String, @Nullable String> environment) {
 		this.loaders = loaders;
 		this.environment = environment;
 	}

core/spring-boot/src/main/java/org/springframework/boot/context/config/SystemEnvironmentConfigDataResource.java

@@ -22,6 +22,8 @@ import java.util.List;
 import java.util.Objects;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.env.PropertySourceLoader;
 import org.springframework.core.env.PropertySource;
 import org.springframework.core.io.ByteArrayResource;
@@ -39,10 +41,10 @@ class SystemEnvironmentConfigDataResource extends ConfigDataResource {
 
 	private final PropertySourceLoader loader;
 
-	private final Function<String, String> environment;
+	private final Function<String, @Nullable String> environment;
 
 	SystemEnvironmentConfigDataResource(String variableName, PropertySourceLoader loader,
-			Function<String, String> environment) {
+			Function<String, @Nullable String> environment) {
 		this.variableName = variableName;
 		this.loader = loader;
 		this.environment = environment;
@@ -56,7 +58,7 @@ class SystemEnvironmentConfigDataResource extends ConfigDataResource {
 		return this.loader;
 	}
 
-	List<PropertySource<?>> load() throws IOException {
+	@Nullable List<PropertySource<?>> load() throws IOException {
 		String content = this.environment.apply(this.variableName);
 		return (content != null) ? this.loader.load(StringUtils.capitalize(toString()), asResource(content)) : null;
 	}

core/spring-boot/src/main/java/org/springframework/boot/context/config/package-info.java

@@ -20,4 +20,7 @@
  *
  * @see org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor
  */
+@NullMarked
 package org.springframework.boot.context.config;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/event/ApplicationFailedEvent.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.event;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.SpringApplication;
 import org.springframework.context.ConfigurableApplicationContext;
 
@@ -29,7 +31,7 @@ import org.springframework.context.ConfigurableApplicationContext;
 @SuppressWarnings("serial")
 public class ApplicationFailedEvent extends SpringApplicationEvent {
 
-	private final ConfigurableApplicationContext context;
+	private final @Nullable ConfigurableApplicationContext context;
 
 	private final Throwable exception;
 
@@ -40,8 +42,8 @@ public class ApplicationFailedEvent extends SpringApplicationEvent {
 	 * @param context the context that was being created (maybe null)
 	 * @param exception the exception that caused the error
 	 */
-	public ApplicationFailedEvent(SpringApplication application, String[] args, ConfigurableApplicationContext context,
-			Throwable exception) {
+	public ApplicationFailedEvent(SpringApplication application, String[] args,
+			@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		super(application, args);
 		this.context = context;
 		this.exception = exception;
@@ -49,9 +51,9 @@ public class ApplicationFailedEvent extends SpringApplicationEvent {
 
 	/**
 	 * Return the application context.
-	 * @return the context
+	 * @return the context or {@code null}
 	 */
-	public ConfigurableApplicationContext getApplicationContext() {
+	public @Nullable ConfigurableApplicationContext getApplicationContext() {
 		return this.context;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/event/ApplicationReadyEvent.java

@@ -18,6 +18,8 @@ package org.springframework.boot.context.event;
 
 import java.time.Duration;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.SpringApplication;
 import org.springframework.context.ConfigurableApplicationContext;
 
@@ -37,7 +39,7 @@ public class ApplicationReadyEvent extends SpringApplicationEvent {
 
 	private final ConfigurableApplicationContext context;
 
-	private final Duration timeTaken;
+	private final @Nullable Duration timeTaken;
 
 	/**
 	 * Create a new {@link ApplicationReadyEvent} instance.
@@ -48,7 +50,7 @@ public class ApplicationReadyEvent extends SpringApplicationEvent {
 	 * @since 2.6.0
 	 */
 	public ApplicationReadyEvent(SpringApplication application, String[] args, ConfigurableApplicationContext context,
-			Duration timeTaken) {
+			@Nullable Duration timeTaken) {
 		super(application, args);
 		this.context = context;
 		this.timeTaken = timeTaken;
@@ -68,7 +70,7 @@ public class ApplicationReadyEvent extends SpringApplicationEvent {
 	 * @return the time taken to be ready to service requests
 	 * @since 2.6.0
 	 */
-	public Duration getTimeTaken() {
+	public @Nullable Duration getTimeTaken() {
 		return this.timeTaken;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/event/ApplicationStartedEvent.java

@@ -18,6 +18,8 @@ package org.springframework.boot.context.event;
 
 import java.time.Duration;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.ApplicationRunner;
 import org.springframework.boot.CommandLineRunner;
 import org.springframework.boot.SpringApplication;
@@ -36,7 +38,7 @@ public class ApplicationStartedEvent extends SpringApplicationEvent {
 
 	private final ConfigurableApplicationContext context;
 
-	private final Duration timeTaken;
+	private final @Nullable Duration timeTaken;
 
 	/**
 	 * Create a new {@link ApplicationStartedEvent} instance.
@@ -47,7 +49,7 @@ public class ApplicationStartedEvent extends SpringApplicationEvent {
 	 * @since 2.6.0
 	 */
 	public ApplicationStartedEvent(SpringApplication application, String[] args, ConfigurableApplicationContext context,
-			Duration timeTaken) {
+			@Nullable Duration timeTaken) {
 		super(application, args);
 		this.context = context;
 		this.timeTaken = timeTaken;
@@ -66,7 +68,7 @@ public class ApplicationStartedEvent extends SpringApplicationEvent {
 	 * @return the startup time
 	 * @since 2.6.0
 	 */
-	public Duration getTimeTaken() {
+	public @Nullable Duration getTimeTaken() {
 		return this.timeTaken;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/event/EventPublishingRunListener.java

@@ -20,6 +20,7 @@ import java.time.Duration;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.ConfigurableBootstrapContext;
 import org.springframework.boot.SpringApplication;
@@ -99,19 +100,19 @@ class EventPublishingRunListener implements SpringApplicationRunListener, Ordere
 	}
 
 	@Override
-	public void started(ConfigurableApplicationContext context, Duration timeTaken) {
+	public void started(ConfigurableApplicationContext context, @Nullable Duration timeTaken) {
 		context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context, timeTaken));
 		AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
 	}
 
 	@Override
-	public void ready(ConfigurableApplicationContext context, Duration timeTaken) {
+	public void ready(ConfigurableApplicationContext context, @Nullable Duration timeTaken) {
 		context.publishEvent(new ApplicationReadyEvent(this.application, this.args, context, timeTaken));
 		AvailabilityChangeEvent.publish(context, ReadinessState.ACCEPTING_TRAFFIC);
 	}
 
 	@Override
-	public void failed(ConfigurableApplicationContext context, Throwable exception) {
+	public void failed(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 		ApplicationFailedEvent event = new ApplicationFailedEvent(this.application, this.args, context, exception);
 		if (context != null && context.isActive()) {
 			// Listeners have been registered to the application context so we should

core/spring-boot/src/main/java/org/springframework/boot/context/event/package-info.java

@@ -18,4 +18,7 @@
  * {@link org.springframework.context.ApplicationEvent ApplicationEvents} triggered by
  * Spring Boot.
  */
+@NullMarked
 package org.springframework.boot.context.event;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/logging/LoggingApplicationListener.java

@@ -25,6 +25,7 @@ import java.util.function.BiConsumer;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.boot.SpringApplication;
@@ -54,6 +55,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;
 import org.springframework.core.log.LogMessage;
+import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.StringUtils;
@@ -181,17 +183,17 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 
 	private final Log logger = LogFactory.getLog(getClass());
 
-	private LoggingSystem loggingSystem;
+	private @Nullable LoggingSystem loggingSystem;
 
-	private LogFile logFile;
+	private @Nullable LogFile logFile;
 
-	private LoggerGroups loggerGroups;
+	private @Nullable LoggerGroups loggerGroups;
 
 	private int order = DEFAULT_ORDER;
 
 	private boolean parseArgs = true;
 
-	private LogLevel springBootLogging = null;
+	private @Nullable LogLevel springBootLogging = null;
 
 	@Override
 	public boolean supportsEventType(ResolvableType resolvableType) {
@@ -199,11 +201,11 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 	}
 
 	@Override
-	public boolean supportsSourceType(Class<?> sourceType) {
+	public boolean supportsSourceType(@Nullable Class<?> sourceType) {
 		return isAssignableFrom(sourceType, SOURCE_TYPES);
 	}
 
-	private boolean isAssignableFrom(Class<?> type, Class<?>... supportedTypes) {
+	private boolean isAssignableFrom(@Nullable Class<?> type, Class<?>... supportedTypes) {
 		if (type != null) {
 			for (Class<?> supportedType : supportedTypes) {
 				if (supportedType.isAssignableFrom(type)) {
@@ -250,6 +252,7 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 		ConfigurableApplicationContext applicationContext = event.getApplicationContext();
 		ConfigurableListableBeanFactory beanFactory = applicationContext.getBeanFactory();
 		if (!beanFactory.containsBean(LOGGING_SYSTEM_BEAN_NAME)) {
+			Assert.state(this.loggingSystem != null, "loggingSystem is not set");
 			beanFactory.registerSingleton(LOGGING_SYSTEM_BEAN_NAME, this.loggingSystem);
 		}
 		if (this.logFile != null && !beanFactory.containsBean(LOG_FILE_BEAN_NAME)) {
@@ -295,6 +298,7 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 		}
 		this.loggerGroups = new LoggerGroups(DEFAULT_GROUP_LOGGERS);
 		initializeEarlyLoggingLevel(environment);
+		Assert.state(this.loggingSystem != null, "loggingSystem is not set");
 		initializeSystem(environment, this.loggingSystem, this.logFile);
 		initializeFinalLoggingLevels(environment, this.loggingSystem);
 		registerShutdownHookIfNecessary(environment, this.loggingSystem);
@@ -321,7 +325,8 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 		return (value != null && !value.equals("false"));
 	}
 
-	private void initializeSystem(ConfigurableEnvironment environment, LoggingSystem system, LogFile logFile) {
+	private void initializeSystem(ConfigurableEnvironment environment, LoggingSystem system,
+			@Nullable LogFile logFile) {
 		String logConfig = environment.getProperty(CONFIG_PROPERTY);
 		if (StringUtils.hasLength(logConfig)) {
 			logConfig = logConfig.strip();
@@ -348,7 +353,7 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 		}
 	}
 
-	private boolean ignoreLogConfig(String logConfig) {
+	private boolean ignoreLogConfig(@Nullable String logConfig) {
 		return !StringUtils.hasLength(logConfig) || logConfig.startsWith("-D");
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/logging/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Logging integration with Spring's Application Context.
  */
+@NullMarked
 package org.springframework.boot.context.logging;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/metrics/buffering/BufferedStartupStep.java

@@ -24,6 +24,8 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.metrics.StartupStep;
 import org.springframework.util.Assert;
 
@@ -41,7 +43,7 @@ class BufferedStartupStep implements StartupStep {
 
 	private final long id;
 
-	private final BufferedStartupStep parent;
+	private final @Nullable BufferedStartupStep parent;
 
 	private final List<Tag> tags = new ArrayList<>();
 
@@ -51,7 +53,7 @@ class BufferedStartupStep implements StartupStep {
 
 	private final AtomicBoolean ended = new AtomicBoolean();
 
-	BufferedStartupStep(BufferedStartupStep parent, String name, long id, Instant startTime,
+	BufferedStartupStep(@Nullable BufferedStartupStep parent, String name, long id, Instant startTime,
 			Consumer<BufferedStartupStep> recorder) {
 		this.parent = parent;
 		this.name = name;
@@ -60,7 +62,7 @@ class BufferedStartupStep implements StartupStep {
 		this.recorder = recorder;
 	}
 
-	BufferedStartupStep getParent() {
+	@Nullable BufferedStartupStep getParent() {
 		return this.parent;
 	}
 
@@ -79,7 +81,7 @@ class BufferedStartupStep implements StartupStep {
 	}
 
 	@Override
-	public Long getParentId() {
+	public @Nullable Long getParentId() {
 		return (this.parent != null) ? this.parent.getId() : null;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/metrics/buffering/BufferingApplicationStartup.java

@@ -26,6 +26,8 @@ import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.metrics.buffering.StartupTimeline.TimelineEvent;
 import org.springframework.core.metrics.ApplicationStartup;
 import org.springframework.core.metrics.StartupStep;
@@ -133,7 +135,7 @@ public class BufferingApplicationStartup implements ApplicationStartup {
 		}
 	}
 
-	private BufferedStartupStep getLatestActive(BufferedStartupStep step) {
+	private @Nullable BufferedStartupStep getLatestActive(@Nullable BufferedStartupStep step) {
 		while (step != null && step.isEnded()) {
 			step = step.getParent();
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/metrics/buffering/package-info.java

@@ -18,4 +18,7 @@
  * {@link org.springframework.core.metrics.ApplicationStartup} implementation for
  * buffering steps and measuring their processing time.
  */
+@NullMarked
 package org.springframework.boot.context.metrics.buffering;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Classes related to Spring's {@link org.springframework.context.ApplicationContext}.
  */
+@NullMarked
 package org.springframework.boot.context;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot/src/main/java/org/springframework/boot/context/properties/BindMethodAttribute.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.properties;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.boot.context.properties.bind.BindMethod;
@@ -36,21 +38,21 @@ final class BindMethodAttribute {
 	private BindMethodAttribute() {
 	}
 
-	static BindMethod get(ApplicationContext applicationContext, String beanName) {
+	static @Nullable BindMethod get(ApplicationContext applicationContext, String beanName) {
 		return (applicationContext instanceof ConfigurableApplicationContext configurableApplicationContext)
 				? get(configurableApplicationContext.getBeanFactory(), beanName) : null;
 	}
 
-	static BindMethod get(ConfigurableListableBeanFactory beanFactory, String beanName) {
+	static @Nullable BindMethod get(ConfigurableListableBeanFactory beanFactory, String beanName) {
 		return (!beanFactory.containsBeanDefinition(beanName)) ? null : get(beanFactory.getBeanDefinition(beanName));
 	}
 
-	static BindMethod get(BeanDefinitionRegistry beanDefinitionRegistry, String beanName) {
+	static @Nullable BindMethod get(BeanDefinitionRegistry beanDefinitionRegistry, String beanName) {
 		return (!beanDefinitionRegistry.containsBeanDefinition(beanName)) ? null
 				: get(beanDefinitionRegistry.getBeanDefinition(beanName));
 	}
 
-	static BindMethod get(AttributeAccessor attributes) {
+	static @Nullable BindMethod get(AttributeAccessor attributes) {
 		return (BindMethod) attributes.getAttribute(NAME);
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/properties/BoundConfigurationProperties.java

@@ -20,6 +20,8 @@ import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
@@ -53,7 +55,7 @@ public class BoundConfigurationProperties {
 	 * @param name the property name
 	 * @return the bound property or {@code null}
 	 */
-	public ConfigurationProperty get(ConfigurationPropertyName name) {
+	public @Nullable ConfigurationProperty get(ConfigurationPropertyName name) {
 		return this.properties.get(name);
 	}
 
@@ -71,7 +73,7 @@ public class BoundConfigurationProperties {
 	 * @param context the context to search
 	 * @return a {@link BoundConfigurationProperties} or {@code null}
 	 */
-	public static BoundConfigurationProperties get(ApplicationContext context) {
+	public static @Nullable BoundConfigurationProperties get(ApplicationContext context) {
 		return (!context.containsBeanDefinition(BEAN_NAME)) ? null
 				: context.getBean(BEAN_NAME, BoundConfigurationProperties.class);
 	}

core/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBean.java

@@ -24,6 +24,8 @@ import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aop.support.AopUtils;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -40,6 +42,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.MergedAnnotation;
 import org.springframework.core.annotation.MergedAnnotations;
 import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
+import org.springframework.lang.Contract;
 import org.springframework.util.Assert;
 import org.springframework.validation.annotation.Validated;
 
@@ -66,11 +69,11 @@ public final class ConfigurationPropertiesBean {
 
 	private final String name;
 
-	private final Object instance;
+	private final @Nullable Object instance;
 
 	private final Bindable<?> bindTarget;
 
-	private ConfigurationPropertiesBean(String name, Object instance, Bindable<?> bindTarget) {
+	private ConfigurationPropertiesBean(String name, @Nullable Object instance, Bindable<?> bindTarget) {
 		this.name = name;
 		this.instance = instance;
 		this.bindTarget = bindTarget;
@@ -88,7 +91,7 @@ public final class ConfigurationPropertiesBean {
 	 * Return the actual Spring bean instance.
 	 * @return the bean instance
 	 */
-	public Object getInstance() {
+	public @Nullable Object getInstance() {
 		return this.instance;
 	}
 
@@ -97,7 +100,9 @@ public final class ConfigurationPropertiesBean {
 	 * @return the bean type
 	 */
 	Class<?> getType() {
-		return this.bindTarget.getType().resolve();
+		Class<?> resolved = this.bindTarget.getType().resolve();
+		Assert.state(resolved != null, "'resolved' must not be null");
+		return resolved;
 	}
 
 	/**
@@ -107,7 +112,9 @@ public final class ConfigurationPropertiesBean {
 	 * @return the configuration properties annotation
 	 */
 	public ConfigurationProperties getAnnotation() {
-		return this.bindTarget.getAnnotation(ConfigurationProperties.class);
+		ConfigurationProperties annotation = this.bindTarget.getAnnotation(ConfigurationProperties.class);
+		Assert.state(annotation != null, "'annotation' must not be null");
+		return annotation;
 	}
 
 	/**
@@ -193,7 +200,8 @@ public final class ConfigurationPropertiesBean {
 	 * factory method are annotated with
 	 * {@link ConfigurationProperties @ConfigurationProperties}
 	 */
-	public static ConfigurationPropertiesBean get(ApplicationContext applicationContext, Object bean, String beanName) {
+	public static @Nullable ConfigurationPropertiesBean get(ApplicationContext applicationContext, Object bean,
+			String beanName) {
 		Method factoryMethod = findFactoryMethod(applicationContext, beanName);
 		Bindable<Object> bindTarget = createBindTarget(bean, bean.getClass(), factoryMethod);
 		if (bindTarget == null) {
@@ -209,18 +217,19 @@ public final class ConfigurationPropertiesBean {
 		return create(beanName, bean, bindTarget);
 	}
 
-	private static Method findFactoryMethod(ApplicationContext applicationContext, String beanName) {
+	private static @Nullable Method findFactoryMethod(ApplicationContext applicationContext, String beanName) {
 		if (applicationContext instanceof ConfigurableApplicationContext configurableContext) {
 			return findFactoryMethod(configurableContext, beanName);
 		}
 		return null;
 	}
 
-	private static Method findFactoryMethod(ConfigurableApplicationContext applicationContext, String beanName) {
+	private static @Nullable Method findFactoryMethod(ConfigurableApplicationContext applicationContext,
+			String beanName) {
 		return findFactoryMethod(applicationContext.getBeanFactory(), beanName);
 	}
 
-	private static Method findFactoryMethod(ConfigurableListableBeanFactory beanFactory, String beanName) {
+	private static @Nullable Method findFactoryMethod(ConfigurableListableBeanFactory beanFactory, String beanName) {
 		if (beanFactory.containsBeanDefinition(beanName)) {
 			BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName);
 			if (beanDefinition instanceof RootBeanDefinition rootBeanDefinition) {
@@ -237,14 +246,16 @@ public final class ConfigurationPropertiesBean {
 		return create(beanName, null, bindTarget.withBindMethod(VALUE_OBJECT_BIND_METHOD));
 	}
 
-	private static Bindable<Object> createBindTarget(Object bean, Class<?> beanType, Method factoryMethod) {
+	private static @Nullable Bindable<Object> createBindTarget(@Nullable Object bean, Class<?> beanType,
+			@Nullable Method factoryMethod) {
 		ResolvableType type = (factoryMethod != null) ? ResolvableType.forMethodReturnType(factoryMethod)
 				: ResolvableType.forClass(beanType);
 		Annotation[] annotations = findAnnotations(bean, beanType, factoryMethod);
 		return (annotations != null) ? Bindable.of(type).withAnnotations(annotations) : null;
 	}
 
-	private static Annotation[] findAnnotations(Object instance, Class<?> type, Method factory) {
+	private static Annotation @Nullable [] findAnnotations(@Nullable Object instance, Class<?> type,
+			@Nullable Method factory) {
 		ConfigurationProperties annotation = findAnnotation(instance, type, factory, ConfigurationProperties.class);
 		if (annotation == null) {
 			return null;
@@ -253,8 +264,8 @@ public final class ConfigurationPropertiesBean {
 		return (validated != null) ? new Annotation[] { annotation, validated } : new Annotation[] { annotation };
 	}
 
-	private static <A extends Annotation> A findAnnotation(Object instance, Class<?> type, Method factory,
-			Class<A> annotationType) {
+	private static <A extends Annotation> @Nullable A findAnnotation(@Nullable Object instance, Class<?> type,
+			@Nullable Method factory, Class<A> annotationType) {
 		MergedAnnotation<A> annotation = MergedAnnotation.missing();
 		if (factory != null) {
 			annotation = findMergedAnnotation(factory, annotationType);
@@ -269,13 +280,15 @@ public final class ConfigurationPropertiesBean {
 		return annotation.isPresent() ? annotation.synthesize() : null;
 	}
 
-	private static <A extends Annotation> MergedAnnotation<A> findMergedAnnotation(AnnotatedElement element,
+	private static <A extends Annotation> MergedAnnotation<A> findMergedAnnotation(@Nullable AnnotatedElement element,
 			Class<A> annotationType) {
 		return (element != null) ? MergedAnnotations.from(element, SearchStrategy.TYPE_HIERARCHY).get(annotationType)
 				: MergedAnnotation.missing();
 	}
 
-	private static ConfigurationPropertiesBean create(String name, Object instance, Bindable<Object> bindTarget) {
+	@Contract("_, _, !null -> !null")
+	private static @Nullable ConfigurationPropertiesBean create(String name, @Nullable Object instance,
+			@Nullable Bindable<Object> bindTarget) {
 		return (bindTarget != null) ? new ConfigurationPropertiesBean(name, instance, bindTarget) : null;
 	}
 
@@ -298,7 +311,7 @@ public final class ConfigurationPropertiesBean {
 	}
 
 	private static org.springframework.boot.context.properties.bind.BindMethod deduceBindMethod(
-			Constructor<?> bindConstructor) {
+			@Nullable Constructor<?> bindConstructor) {
 		return (bindConstructor != null) ? VALUE_OBJECT_BIND_METHOD : JAVA_BEAN_BIND_METHOD;
 	}
 

core/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBeanFactoryInitializationAotProcessor.java

@@ -19,6 +19,8 @@ package org.springframework.boot.context.properties;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.generate.GenerationContext;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotContribution;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor;
@@ -41,7 +43,7 @@ import org.springframework.util.ClassUtils;
 class ConfigurationPropertiesBeanFactoryInitializationAotProcessor implements BeanFactoryInitializationAotProcessor {
 
 	@Override
-	public ConfigurationPropertiesReflectionHintsContribution processAheadOfTime(
+	public @Nullable ConfigurationPropertiesReflectionHintsContribution processAheadOfTime(
 			ConfigurableListableBeanFactory beanFactory) {
 		String[] beanNames = beanFactory.getBeanNamesForAnnotation(ConfigurationProperties.class);
 		List<Bindable<?>> bindables = new ArrayList<>();

core/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBeanRegistrationAotProcessor.java

@@ -20,6 +20,8 @@ import java.util.function.Predicate;
 
 import javax.lang.model.element.Modifier;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.generate.GeneratedMethod;
 import org.springframework.aot.generate.GenerationContext;
 import org.springframework.beans.factory.BeanFactory;
@@ -45,7 +47,7 @@ import org.springframework.javapoet.CodeBlock;
 class ConfigurationPropertiesBeanRegistrationAotProcessor implements BeanRegistrationAotProcessor {
 
 	@Override
-	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
+	public @Nullable BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
 		if (!isImmutableConfigurationPropertiesBeanDefinition(registeredBean.getMergedBeanDefinition())) {
 			return null;
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBinder.java

@@ -20,6 +20,8 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.PropertyEditorRegistry;
 import org.springframework.beans.factory.BeanFactory;
@@ -72,13 +74,13 @@ class ConfigurationPropertiesBinder {
 
 	private final PropertySources propertySources;
 
-	private final Validator configurationPropertiesValidator;
+	private final @Nullable Validator configurationPropertiesValidator;
 
 	private final boolean jsr303Present;
 
-	private volatile List<ConfigurationPropertiesBindHandlerAdvisor> bindHandlerAdvisors;
+	private volatile @Nullable List<ConfigurationPropertiesBindHandlerAdvisor> bindHandlerAdvisors;
 
-	private volatile Binder binder;
+	private volatile @Nullable Binder binder;
 
 	ConfigurationPropertiesBinder(ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;
@@ -101,7 +103,7 @@ class ConfigurationPropertiesBinder {
 		return getBinder().bindOrCreate(annotation.prefix(), target, bindHandler);
 	}
 
-	private Validator getConfigurationPropertiesValidator(ApplicationContext applicationContext) {
+	private @Nullable Validator getConfigurationPropertiesValidator(ApplicationContext applicationContext) {
 		if (applicationContext.containsBean(VALIDATOR_BEAN_NAME)) {
 			return applicationContext.getBean(VALIDATOR_BEAN_NAME, Validator.class);
 		}
@@ -153,7 +155,9 @@ class ConfigurationPropertiesBinder {
 			validators.add(this.configurationPropertiesValidator);
 		}
 		if (this.jsr303Present && target.getAnnotation(Validated.class) != null) {
-			validators.add(getJsr303Validator(target.getType().resolve()));
+			Class<?> resolved = target.getType().resolve();
+			Assert.state(resolved != null, "'resolved' must not be null");
+			validators.add(getJsr303Validator(resolved));
 		}
 		Validator selfValidator = getSelfValidator(target);
 		if (selfValidator != null) {
@@ -162,7 +166,7 @@ class ConfigurationPropertiesBinder {
 		return validators;
 	}
 
-	private Validator getSelfValidator(Bindable<?> target) {
+	private @Nullable Validator getSelfValidator(Bindable<?> target) {
 		if (target.getValue() != null) {
 			Object value = target.getValue().get();
 			return (value instanceof Validator validator) ? validator : null;
@@ -194,11 +198,11 @@ class ConfigurationPropertiesBinder {
 		return new PropertySourcesPlaceholdersResolver(this.propertySources);
 	}
 
-	private List<ConversionService> getConversionServices() {
+	private @Nullable List<ConversionService> getConversionServices() {
 		return new ConversionServiceDeducer(this.applicationContext).getConversionServices();
 	}
 
-	private Consumer<PropertyEditorRegistry> getPropertyEditorInitializer() {
+	private @Nullable Consumer<PropertyEditorRegistry> getPropertyEditorInitializer() {
 		if (this.applicationContext instanceof ConfigurableApplicationContext configurableContext) {
 			return configurableContext.getBeanFactory()::copyRegisteredEditorsTo;
 		}
@@ -235,7 +239,7 @@ class ConfigurationPropertiesBinder {
 					? target.withBindRestrictions(BindRestriction.NO_DIRECT_PROPERTY) : target;
 		}
 
-		private boolean isConfigurationProperties(Class<?> target) {
+		private boolean isConfigurationProperties(@Nullable Class<?> target) {
 			return target != null && MergedAnnotations.from(target).isPresent(ConfigurationProperties.class);
 		}
 
@@ -247,7 +251,7 @@ class ConfigurationPropertiesBinder {
 	static class ConfigurationPropertiesBinderFactory
 			implements FactoryBean<ConfigurationPropertiesBinder>, ApplicationContextAware {
 
-		private ConfigurationPropertiesBinder binder;
+		private @Nullable ConfigurationPropertiesBinder binder;
 
 		@Override
 		public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {

core/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBindingPostProcessor.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.context.properties;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -49,10 +51,13 @@ public class ConfigurationPropertiesBindingPostProcessor
 	 */
 	public static final String BEAN_NAME = ConfigurationPropertiesBindingPostProcessor.class.getName();
 
+	@SuppressWarnings("NullAway.Init")
 	private ApplicationContext applicationContext;
 
+	@SuppressWarnings("NullAway.Init")
 	private BeanDefinitionRegistry registry;
 
+	@SuppressWarnings("NullAway.Init")
 	private ConfigurationPropertiesBinder binder;
 
 	@Override
@@ -85,7 +90,7 @@ public class ConfigurationPropertiesBindingPostProcessor
 		return BindMethod.VALUE_OBJECT.equals(BindMethodAttribute.get(this.registry, beanName));
 	}
 
-	private void bind(ConfigurationPropertiesBean bean) {
+	private void bind(@Nullable ConfigurationPropertiesBean bean) {
 		if (bean == null) {
 			return;
 		}

core/spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesCharSequenceToObjectConverter.java

@@ -19,6 +19,8 @@ package org.springframework.boot.context.properties;
 import java.util.Collections;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.convert.ApplicationConversionService;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
@@ -96,7 +98,10 @@ final class ConfigurationPropertiesCharSequenceToObjectConverter implements Cond
 	}
 
 	@Override
-	public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
+	public @Nullable Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
+		if (source == null) {
+			return null;
+		}
 		return this.conversionService.convert(source.toString(), STRING, targetType);
 	}