Add nullability annotations to tests in module/spring-boot-devtools

See gh-47263

module/spring-boot-devtools/build.gradle

@@ -118,3 +118,12 @@ tasks.register("syncIntTestDependencies", Sync) {
 intTest {
 	dependsOn syncIntTestDependencies
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}
+
+tasks.named("compileIntTestJava") {
+	options.nullability.checking = "tests"
+}
+

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/autoconfigure/AbstractDevToolsDataSourceAutoConfigurationTests.java

@@ -25,6 +25,7 @@ import java.util.function.Supplier;
 
 import javax.sql.DataSource;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.AnnotatedGenericBeanDefinition;
@@ -35,6 +36,7 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.BDDMockito.then;
 import static org.mockito.BDDMockito.willReturn;
@@ -99,18 +101,21 @@ abstract class AbstractDevToolsDataSourceAutoConfigurationTests {
 		});
 		thread.start();
 		thread.join();
-		return atomicReference.get();
+		ConfigurableApplicationContext context = atomicReference.get();
+		assertThat(context).isNotNull();
+		return context;
 	}
 
 	protected final ConfigurableApplicationContext createContext(Class<?>... classes) {
 		return createContext(null, classes);
 	}
 
-	protected final ConfigurableApplicationContext createContext(String driverClassName, Class<?>... classes) {
+	protected final ConfigurableApplicationContext createContext(@Nullable String driverClassName,
+			Class<?>... classes) {
 		return createContext(driverClassName, null, classes);
 	}
 
-	protected final ConfigurableApplicationContext createContext(String driverClassName, String url,
+	protected final ConfigurableApplicationContext createContext(@Nullable String driverClassName, @Nullable String url,
 			Class<?>... classes) {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 		context.register(classes);

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/autoconfigure/DevToolsR2dbcAutoConfigurationTests.java

@@ -24,6 +24,7 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
 import io.r2dbc.spi.ConnectionFactory;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -125,14 +126,16 @@ class DevToolsR2dbcAutoConfigurationTests {
 			});
 			thread.start();
 			thread.join();
-			return atomicReference.get();
+			ConfigurableApplicationContext context = atomicReference.get();
+			assertThat(context).isNotNull();
+			return context;
 		}
 
 		protected final ConfigurableApplicationContext createContext(Class<?>... classes) {
 			return createContext(null, classes);
 		}
 
-		protected final ConfigurableApplicationContext createContext(String url, Class<?>... classes) {
+		protected final ConfigurableApplicationContext createContext(@Nullable String url, Class<?>... classes) {
 			AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 			if (!ObjectUtils.isEmpty(classes)) {
 				context.register(classes);

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/autoconfigure/LocalDevToolsAutoConfigurationTests.java

@@ -26,6 +26,7 @@ import java.util.function.Supplier;
 import org.apache.catalina.Container;
 import org.apache.catalina.core.StandardWrapper;
 import org.apache.jasper.EmbeddedServletOptions;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -74,7 +75,7 @@ import static org.mockito.Mockito.reset;
 @ExtendWith(MockRestarter.class)
 class LocalDevToolsAutoConfigurationTests {
 
-	private ConfigurableApplicationContext context;
+	private @Nullable ConfigurableApplicationContext context;
 
 	@AfterEach
 	void cleanup() {
@@ -152,8 +153,10 @@ class LocalDevToolsAutoConfigurationTests {
 		Map<String, Object> properties = new HashMap<>();
 		properties.put("spring.devtools.livereload.enabled", false);
 		this.context = getContext(() -> initializeAndRun(Config.class, properties));
-		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean(OptionalLiveReloadServer.class));
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class).isThrownBy(() -> {
+			assertThat(this.context).isNotNull();
+			this.context.getBean(OptionalLiveReloadServer.class);
+		});
 	}
 
 	@Test
@@ -184,8 +187,10 @@ class LocalDevToolsAutoConfigurationTests {
 		Map<String, Object> properties = new HashMap<>();
 		properties.put("spring.devtools.restart.enabled", false);
 		this.context = getContext(() -> initializeAndRun(Config.class, properties));
-		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean(ClassPathFileSystemWatcher.class));
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class).isThrownBy(() -> {
+			assertThat(this.context).isNotNull();
+			this.context.getBean(ClassPathFileSystemWatcher.class);
+		});
 	}
 
 	@Test
@@ -195,7 +200,9 @@ class LocalDevToolsAutoConfigurationTests {
 		this.context = getContext(() -> initializeAndRun(Config.class, properties));
 		ClassPathFileSystemWatcher classPathWatcher = this.context.getBean(ClassPathFileSystemWatcher.class);
 		Object watcher = ReflectionTestUtils.getField(classPathWatcher, "fileSystemWatcher");
+		assertThat(watcher).isNotNull();
 		Object filter = ReflectionTestUtils.getField(watcher, "triggerFilter");
+		assertThat(filter).isNotNull();
 		assertThat(filter).isInstanceOf(TriggerFileFilter.class);
 	}
 
@@ -206,6 +213,7 @@ class LocalDevToolsAutoConfigurationTests {
 		this.context = getContext(() -> initializeAndRun(Config.class, properties));
 		ClassPathFileSystemWatcher classPathWatcher = this.context.getBean(ClassPathFileSystemWatcher.class);
 		Object watcher = ReflectionTestUtils.getField(classPathWatcher, "fileSystemWatcher");
+		assertThat(watcher).isNotNull();
 		@SuppressWarnings("unchecked")
 		Map<File, Object> directories = (Map<File, Object>) ReflectionTestUtils.getField(watcher, "directories");
 		assertThat(directories).hasSize(2)
@@ -218,10 +226,12 @@ class LocalDevToolsAutoConfigurationTests {
 		this.context = getContext(() -> initializeAndRun(Config.class));
 		TomcatWebServer tomcatContainer = (TomcatWebServer) ((ServletWebServerApplicationContext) this.context)
 			.getWebServer();
+		assertThat(tomcatContainer).isNotNull();
 		Container context = tomcatContainer.getTomcat().getHost().findChildren()[0];
 		StandardWrapper jspServletWrapper = (StandardWrapper) context.findChild("jsp");
 		EmbeddedServletOptions options = (EmbeddedServletOptions) ReflectionTestUtils
 			.getField(jspServletWrapper.getServlet(), "options");
+		assertThat(options).isNotNull();
 		assertThat(options.getDevelopment()).isTrue();
 	}
 
@@ -234,7 +244,9 @@ class LocalDevToolsAutoConfigurationTests {
 		});
 		thread.start();
 		thread.join();
-		return atomicReference.get();
+		ConfigurableApplicationContext context = atomicReference.get();
+		assertThat(context).isNotNull();
+		return context;
 	}
 
 	private ConfigurableApplicationContext initializeAndRun(Class<?> config, String... args) {

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/autoconfigure/RemoteDevToolsAutoConfigurationTests.java

@@ -20,6 +20,7 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
 import jakarta.servlet.Filter;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -65,7 +66,7 @@ class RemoteDevToolsAutoConfigurationTests {
 
 	private static final String DEFAULT_SECRET_HEADER_NAME = RemoteDevToolsProperties.DEFAULT_SECRET_HEADER_NAME;
 
-	private AnnotationConfigServletWebApplicationContext context;
+	private @Nullable AnnotationConfigServletWebApplicationContext context;
 
 	private MockHttpServletRequest request;
 
@@ -90,8 +91,10 @@ class RemoteDevToolsAutoConfigurationTests {
 	@Test
 	void disabledIfRemoteSecretIsMissing() throws Exception {
 		this.context = getContext(() -> loadContext("a:b"));
-		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean(DispatcherFilter.class));
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class).isThrownBy(() -> {
+			assertThat(this.context).isNotNull();
+			this.context.getBean(DispatcherFilter.class);
+		});
 	}
 
 	@Test
@@ -182,8 +185,10 @@ class RemoteDevToolsAutoConfigurationTests {
 	void disableRestart() throws Exception {
 		this.context = getContext(() -> loadContext("spring.devtools.remote.secret:supersecret",
 				"spring.devtools.remote.restart.enabled:false"));
-		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean("remoteRestartHandlerMapper"));
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class).isThrownBy(() -> {
+			assertThat(this.context).isNotNull();
+			this.context.getBean("remoteRestartHandlerMapper");
+		});
 	}
 
 	@Test
@@ -218,10 +223,13 @@ class RemoteDevToolsAutoConfigurationTests {
 		});
 		thread.start();
 		thread.join();
-		return atomicReference.get();
+		AnnotationConfigServletWebApplicationContext context = atomicReference.get();
+		assertThat(context).isNotNull();
+		return context;
 	}
 
 	private void assertRestartInvoked(boolean value) {
+		assertThat(this.context).isNotNull();
 		assertThat(this.context.getBean(MockHttpRestartServer.class).invoked).isEqualTo(value);
 	}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/autoconfigure/TriggerFileFilterTests.java

@@ -32,9 +32,11 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
 class TriggerFileFilterTests {
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	File tempDir;
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void nameMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new TriggerFileFilter(null))
 			.withMessageContaining("'name' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/classpath/ClassPathChangedEventTests.java

@@ -36,6 +36,7 @@ class ClassPathChangedEventTests {
 	private final Object source = new Object();
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void changeSetMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassPathChangedEvent(this.source, null, false))
 			.withMessageContaining("'changeSet' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/classpath/ClassPathFileChangeListenerTests.java

@@ -47,15 +47,19 @@ import static org.mockito.Mockito.never;
 class ClassPathFileChangeListenerTests {
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ApplicationEventPublisher eventPublisher;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClassPathRestartStrategy restartStrategy;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private FileSystemWatcher fileSystemWatcher;
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void eventPublisherMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new ClassPathFileChangeListener(null, this.restartStrategy, this.fileSystemWatcher))
@@ -63,6 +67,7 @@ class ClassPathFileChangeListenerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void restartStrategyMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new ClassPathFileChangeListener(this.eventPublisher, null, this.fileSystemWatcher))

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/classpath/ClassPathFileSystemWatcherTests.java

@@ -51,6 +51,7 @@ import static org.mockito.Mockito.mock;
 class ClassPathFileSystemWatcherTests {
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void urlsMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new ClassPathFileSystemWatcher(mock(FileSystemWatcherFactory.class),
@@ -100,6 +101,7 @@ class ClassPathFileSystemWatcherTests {
 		ClassPathFileSystemWatcher watcher(ClassPathRestartStrategy restartStrategy) {
 			FileSystemWatcher watcher = new FileSystemWatcher(false, Duration.ofMillis(100), Duration.ofMillis(10));
 			URL[] urls = this.environment.getProperty("urls", URL[].class);
+			assertThat(urls).isNotNull();
 			return new ClassPathFileSystemWatcher(new MockFileSystemWatcherFactory(watcher), restartStrategy, urls);
 		}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/classpath/PatternClassPathRestartStrategyTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.devtools.classpath;
 
 import java.io.File;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.devtools.filewatch.ChangedFile;
@@ -82,7 +83,7 @@ class PatternClassPathRestartStrategyTests {
 		assertRestartRequired(strategy, "com/example/Example.class", true);
 	}
 
-	private ClassPathRestartStrategy createStrategy(String pattern) {
+	private ClassPathRestartStrategy createStrategy(@Nullable String pattern) {
 		return new PatternClassPathRestartStrategy(pattern);
 	}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/env/DevToolPropertiesIntegrationTests.java

@@ -22,6 +22,7 @@ import java.util.Locale;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -48,7 +49,7 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
  */
 class DevToolPropertiesIntegrationTests {
 
-	private ConfigurableApplicationContext context;
+	private @Nullable ConfigurableApplicationContext context;
 
 	@BeforeEach
 	void setup() {
@@ -86,8 +87,10 @@ class DevToolPropertiesIntegrationTests {
 		SpringApplication application = new SpringApplication(BeanConditionConfiguration.class);
 		application.setWebApplicationType(WebApplicationType.NONE);
 		this.context = getContext(application::run);
-		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean(MyBean.class));
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class).isThrownBy(() -> {
+			assertThat(this.context).isNotNull();
+			this.context.getBean(MyBean.class);
+		});
 	}
 
 	@Test
@@ -124,7 +127,9 @@ class DevToolPropertiesIntegrationTests {
 		});
 		thread.start();
 		thread.join();
-		return atomicReference.get();
+		ConfigurableApplicationContext context = atomicReference.get();
+		assertThat(context).isNotNull();
+		return context;
 	}
 
 	@Configuration(proxyBeanMethods = false)

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/env/DevToolsHomePropertiesPostProcessorTests.java

@@ -25,10 +25,12 @@ import java.util.Collections;
 import java.util.Map;
 import java.util.Properties;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
+import org.springframework.boot.SpringApplication;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.mock.env.MockEnvironment;
@@ -201,8 +203,8 @@ class DevToolsHomePropertiesPostProcessorTests {
 		return getPostProcessedEnvironment(env, null);
 	}
 
-	private ConfigurableEnvironment getPostProcessedEnvironment(Map<String, String> env, Properties systemProperties)
-			throws Exception {
+	private ConfigurableEnvironment getPostProcessedEnvironment(@Nullable Map<String, String> env,
+			@Nullable Properties systemProperties) throws Exception {
 		if (systemProperties == null) {
 			systemProperties = new Properties();
 			systemProperties.setProperty("user.home", this.home.getAbsolutePath());
@@ -210,7 +212,7 @@ class DevToolsHomePropertiesPostProcessorTests {
 		ConfigurableEnvironment environment = new MockEnvironment();
 		DevToolsHomePropertiesPostProcessor postProcessor = new DevToolsHomePropertiesPostProcessor(
 				(env != null) ? env : Collections.emptyMap(), systemProperties);
-		runPostProcessor(() -> postProcessor.postProcessEnvironment(environment, null));
+		runPostProcessor(() -> postProcessor.postProcessEnvironment(environment, new SpringApplication()));
 		return environment;
 	}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/filewatch/ChangedFileTests.java

@@ -34,9 +34,11 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
 class ChangedFileTests {
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	File tempDir;
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void sourceDirectoryMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new ChangedFile(null, new File(this.tempDir, "file"), Type.ADD))
@@ -44,6 +46,7 @@ class ChangedFileTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void fileMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new ChangedFile(new File(this.tempDir, "directory"), null, Type.ADD))
@@ -51,6 +54,7 @@ class ChangedFileTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void typeMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/filewatch/DirectorySnapshotTests.java

@@ -38,6 +38,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
 class DirectorySnapshotTests {
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	File tempDir;
 
 	private File directory;
@@ -51,6 +52,7 @@ class DirectorySnapshotTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void directoryMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new DirectorySnapshot(null))
 			.withMessageContaining("'directory' must not be null");
@@ -101,6 +103,7 @@ class DirectorySnapshotTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void getChangedFilesSnapshotMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> this.initialSnapshot.getChangedFiles(null, null))
 			.withMessageContaining("'snapshot' must not be null");
@@ -142,7 +145,7 @@ class DirectorySnapshotTests {
 				return changedFile;
 			}
 		}
-		return null;
+		throw new AssertionError("File '%s' not found".formatted(file));
 	}
 
 	private File createTestDirectoryStructure() throws IOException {

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/filewatch/FileSnapshotTests.java

@@ -42,9 +42,11 @@ class FileSnapshotTests {
 	private static final long MODIFIED = new Date().getTime() - TimeUnit.DAYS.toMillis(10);
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	File tempDir;
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void fileMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new FileSnapshot(null))
 			.withMessageContaining("'file' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/filewatch/FileSystemWatcherTests.java

@@ -28,6 +28,7 @@ import java.util.Set;
 import java.util.UUID;
 import java.util.stream.Collectors;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -53,11 +54,12 @@ class FileSystemWatcherTests {
 	private final List<Set<ChangedFiles>> changes = Collections.synchronizedList(new ArrayList<>());
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	File tempDir;
 
 	@BeforeEach
 	void setup() {
-		setupWatcher(20, 10);
+		this.watcher = setupWatcher(20, 10);
 	}
 
 	@Test
@@ -82,6 +84,7 @@ class FileSystemWatcherTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void listenerMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> this.watcher.addListener(null))
 			.withMessageContaining("'fileChangeListener' must not be null");
@@ -95,6 +98,7 @@ class FileSystemWatcherTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void sourceDirectoryMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> this.watcher.addSourceDirectory(null))
 			.withMessageContaining("'directory' must not be null");
@@ -149,7 +153,7 @@ class FileSystemWatcherTests {
 
 	@Test
 	void waitsForPollingInterval() throws Exception {
-		setupWatcher(10, 1);
+		this.watcher = setupWatcher(10, 1);
 		File directory = startWithNewDirectory();
 		touch(new File(directory, "test1.txt"));
 		while (this.changes.size() != 1) {
@@ -162,7 +166,7 @@ class FileSystemWatcherTests {
 
 	@Test
 	void waitsForQuietPeriod() throws Exception {
-		setupWatcher(300, 200);
+		this.watcher = setupWatcher(300, 200);
 		File directory = startWithNewDirectory();
 		for (int i = 0; i < 100; i++) {
 			touch(new File(directory, i + "test.txt"));
@@ -270,7 +274,7 @@ class FileSystemWatcherTests {
 	@Test
 	void withSnapshotRepository() throws Exception {
 		SnapshotStateRepository repository = new TestSnapshotStateRepository();
-		setupWatcher(20, 10, repository);
+		this.watcher = setupWatcher(20, 10, repository);
 		File directory = new File(this.tempDir, UUID.randomUUID().toString());
 		directory.mkdir();
 		File file = touch(new File(directory, "file.txt"));
@@ -280,7 +284,7 @@ class FileSystemWatcherTests {
 		this.watcher.stopAfter(1);
 		this.changes.clear();
 		File recreate = touch(new File(directory, "file.txt"));
-		setupWatcher(20, 10, repository);
+		this.watcher = setupWatcher(20, 10, repository);
 		this.watcher.addSourceDirectory(directory);
 		this.watcher.start();
 		this.watcher.stopAfter(1);
@@ -290,14 +294,16 @@ class FileSystemWatcherTests {
 		assertThat(actual).isEqualTo(expected);
 	}
 
-	private void setupWatcher(long pollingInterval, long quietPeriod) {
-		setupWatcher(pollingInterval, quietPeriod, null);
+	private FileSystemWatcher setupWatcher(long pollingInterval, long quietPeriod) {
+		return setupWatcher(pollingInterval, quietPeriod, null);
 	}
 
-	private void setupWatcher(long pollingInterval, long quietPeriod, SnapshotStateRepository snapshotStateRepository) {
-		this.watcher = new FileSystemWatcher(false, Duration.ofMillis(pollingInterval), Duration.ofMillis(quietPeriod),
-				snapshotStateRepository);
-		this.watcher.addListener(FileSystemWatcherTests.this.changes::add);
+	private FileSystemWatcher setupWatcher(long pollingInterval, long quietPeriod,
+			@Nullable SnapshotStateRepository snapshotStateRepository) {
+		FileSystemWatcher watcher = new FileSystemWatcher(false, Duration.ofMillis(pollingInterval),
+				Duration.ofMillis(quietPeriod), snapshotStateRepository);
+		watcher.addListener(FileSystemWatcherTests.this.changes::add);
+		return watcher;
 	}
 
 	private File startWithNewDirectory() {
@@ -328,7 +334,7 @@ class FileSystemWatcherTests {
 
 	private static final class TestSnapshotStateRepository implements SnapshotStateRepository {
 
-		private Object state;
+		private @Nullable Object state;
 
 		@Override
 		public void save(Object state) {
@@ -336,7 +342,7 @@ class FileSystemWatcherTests {
 		}
 
 		@Override
-		public Object restore() {
+		public @Nullable Object restore() {
 			return this.state;
 		}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/livereload/FrameTests.java

@@ -34,12 +34,14 @@ import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 class FrameTests {
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void payloadMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new Frame((String) null))
 			.withMessageContaining("'payload' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void typeMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new Frame((Frame.Type) null))
 			.withMessageContaining("'type' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/livereload/LiveReloadServerTests.java

@@ -47,11 +47,13 @@ import jakarta.websocket.HandshakeResponse;
 import jakarta.websocket.WebSocketContainer;
 import org.apache.tomcat.websocket.WsWebSocketContainer;
 import org.awaitility.Awaitility;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.http.HttpHeaders;
 import org.springframework.web.client.RestTemplate;
 import org.springframework.web.socket.CloseStatus;
@@ -223,7 +225,7 @@ class LiveReloadServerTests {
 
 	class LiveReloadWebSocketHandler extends TextWebSocketHandler {
 
-		private volatile WebSocketSession session;
+		private volatile @Nullable WebSocketSession session;
 
 		private final CountDownLatch helloLatch = new CountDownLatch(2);
 
@@ -231,7 +233,7 @@ class LiveReloadServerTests {
 
 		private final AtomicInteger pongCount = new AtomicInteger();
 
-		private volatile CloseStatus closeStatus;
+		private volatile @Nullable CloseStatus closeStatus;
 
 		@Override
 		public void afterConnectionEstablished(WebSocketSession session) throws Exception {
@@ -264,11 +266,15 @@ class LiveReloadServerTests {
 		}
 
 		void sendMessage(WebSocketMessage<?> message) throws IOException {
-			this.session.sendMessage(message);
+			WebSocketSession session = this.session;
+			assertThat(session).isNotNull();
+			session.sendMessage(message);
 		}
 
 		void close() throws IOException {
-			this.session.close();
+			WebSocketSession session = this.session;
+			assertThat(session).isNotNull();
+			session.close();
 		}
 
 		List<String> getMessages() {
@@ -279,7 +285,7 @@ class LiveReloadServerTests {
 			return this.pongCount.get();
 		}
 
-		CloseStatus getCloseStatus() {
+		@Nullable CloseStatus getCloseStatus() {
 			return this.closeStatus;
 		}
 
@@ -314,7 +320,9 @@ class LiveReloadServerTests {
 				this.webSocketContainer.connectToServer(endpoint, endpointConfig, uri);
 				return session;
 			};
-			return getTaskExecutor().submitCompletable(connectTask);
+			AsyncTaskExecutor taskExecutor = getTaskExecutor();
+			assertThat(taskExecutor).isNotNull();
+			return taskExecutor.submitCompletable(connectTask);
 		}
 
 		private InetAddress getLocalHost() {

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/client/ClassPathChangeUploaderTests.java

@@ -26,6 +26,7 @@ import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -65,6 +66,7 @@ class ClassPathChangeUploaderTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void urlMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassPathChangeUploader(null, this.requestFactory))
 			.withMessageContaining("'url' must not be empty");
@@ -77,6 +79,7 @@ class ClassPathChangeUploaderTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void requestFactoryMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new ClassPathChangeUploader("http://localhost:8080", null))
@@ -124,7 +127,7 @@ class ClassPathChangeUploaderTests {
 		assertThat(classFiles.hasNext()).isFalse();
 	}
 
-	private void assertClassFile(ClassLoaderFile file, String content, Kind kind) {
+	private void assertClassFile(ClassLoaderFile file, @Nullable String content, Kind kind) {
 		assertThat(file.getContents()).isEqualTo((content != null) ? content.getBytes() : null);
 		assertThat(file.getKind()).isEqualTo(kind);
 	}

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/client/DelayedLiveReloadTriggerTests.java

@@ -49,21 +49,27 @@ class DelayedLiveReloadTriggerTests {
 	private static final String URL = "http://localhost:8080";
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private OptionalLiveReloadServer liveReloadServer;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpRequestFactory requestFactory;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpRequest errorRequest;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpRequest okRequest;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpResponse errorResponse;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpResponse okResponse;
 
 	private DelayedLiveReloadTrigger trigger;
@@ -74,6 +80,7 @@ class DelayedLiveReloadTriggerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void liveReloadServerMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new DelayedLiveReloadTrigger(null, this.requestFactory, URL))
@@ -81,6 +88,7 @@ class DelayedLiveReloadTriggerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void requestFactoryMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new DelayedLiveReloadTrigger(this.liveReloadServer, null, URL))
@@ -88,6 +96,7 @@ class DelayedLiveReloadTriggerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void urlMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new DelayedLiveReloadTrigger(this.liveReloadServer, this.requestFactory, null))

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/client/HttpHeaderInterceptorTests.java

@@ -54,9 +54,11 @@ class HttpHeaderInterceptorTests {
 	private byte[] body;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpRequestExecution execution;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private ClientHttpResponse response;
 
 	private MockHttpServletRequest httpRequest;
@@ -72,6 +74,7 @@ class HttpHeaderInterceptorTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void constructorNullHeaderName() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpHeaderInterceptor(null, this.value))
 			.withMessageContaining("'name' must not be empty");
@@ -84,6 +87,7 @@ class HttpHeaderInterceptorTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void constructorNullHeaderValue() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpHeaderInterceptor(this.name, null))
 			.withMessageContaining("'value' must not be empty");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/client/RemoteClientConfigurationTests.java

@@ -22,6 +22,7 @@ import java.util.HashSet;
 import java.util.Set;
 
 import org.awaitility.Awaitility;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -41,6 +42,7 @@ import org.springframework.boot.test.system.CapturedOutput;
 import org.springframework.boot.test.system.OutputCaptureExtension;
 import org.springframework.boot.test.util.TestPropertyValues;
 import org.springframework.boot.tomcat.servlet.TomcatServletWebServerFactory;
+import org.springframework.boot.web.server.WebServer;
 import org.springframework.boot.web.server.servlet.context.AnnotationConfigServletWebServerApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
@@ -63,9 +65,9 @@ import static org.mockito.Mockito.mock;
 @ExtendWith({ OutputCaptureExtension.class, MockRestarter.class })
 class RemoteClientConfigurationTests {
 
-	private AnnotationConfigServletWebServerApplicationContext context;
+	private @Nullable AnnotationConfigServletWebServerApplicationContext context;
 
-	private AnnotationConfigApplicationContext clientContext;
+	private @Nullable AnnotationConfigApplicationContext clientContext;
 
 	@AfterEach
 	void cleanup() {
@@ -106,6 +108,7 @@ class RemoteClientConfigurationTests {
 		configure();
 		Set<ChangedFiles> changeSet = new HashSet<>();
 		ClassPathChangedEvent event = new ClassPathChangedEvent(this, changeSet, false);
+		assertThat(this.clientContext).isNotNull();
 		this.clientContext.publishEvent(event);
 		LiveReloadServer server = this.clientContext.getBean(LiveReloadServer.class);
 		Awaitility.await().atMost(Duration.ofMinutes(1)).untilAsserted(() -> then(server).should().triggerReload());
@@ -115,20 +118,26 @@ class RemoteClientConfigurationTests {
 	void liveReloadDisabled() {
 		configure("spring.devtools.livereload.enabled:false");
 		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean(OptionalLiveReloadServer.class));
+			.isThrownBy(() -> getContext().getBean(OptionalLiveReloadServer.class));
 	}
 
 	@Test
 	void remoteRestartDisabled() {
 		configure("spring.devtools.remote.restart.enabled:false");
 		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.context.getBean(ClassPathFileSystemWatcher.class));
+			.isThrownBy(() -> getContext().getBean(ClassPathFileSystemWatcher.class));
 	}
 
 	private void configure(String... pairs) {
 		configure("http://localhost", true, pairs);
 	}
 
+	private AnnotationConfigServletWebServerApplicationContext getContext() {
+		AnnotationConfigServletWebServerApplicationContext context = this.context;
+		assertThat(context).isNotNull();
+		return context;
+	}
+
 	private void configure(String remoteUrl, boolean setSecret, String... pairs) {
 		this.context = new AnnotationConfigServletWebServerApplicationContext();
 		this.context.register(Config.class);
@@ -143,7 +152,9 @@ class RemoteClientConfigurationTests {
 		if (setSecret) {
 			TestPropertyValues.of("spring.devtools.remote.secret:secret").applyTo(this.clientContext);
 		}
-		String remoteUrlProperty = "remoteUrl:" + remoteUrl + ":" + this.context.getWebServer().getPort();
+		WebServer webServer = this.context.getWebServer();
+		assertThat(webServer).isNotNull();
+		String remoteUrlProperty = "remoteUrl:" + remoteUrl + ":" + webServer.getPort();
 		TestPropertyValues.of(remoteUrlProperty).applyTo(this.clientContext);
 		this.clientContext.refresh();
 	}

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/server/DispatcherFilterTests.java

@@ -51,9 +51,11 @@ import static org.mockito.Mockito.mock;
 class DispatcherFilterTests {
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private Dispatcher dispatcher;
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private FilterChain chain;
 
 	private DispatcherFilter filter;
@@ -64,6 +66,7 @@ class DispatcherFilterTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void dispatcherMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new DispatcherFilter(null))
 			.withMessageContaining("'dispatcher' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/server/DispatcherTests.java

@@ -52,6 +52,7 @@ import static org.mockito.Mockito.withSettings;
 class DispatcherTests {
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private AccessManager accessManager;
 
 	private final MockHttpServletResponse response = new MockHttpServletResponse();
@@ -61,12 +62,14 @@ class DispatcherTests {
 	private final ServerHttpResponse serverResponse = new ServletServerHttpResponse(this.response);
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void accessManagerMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new Dispatcher(null, Collections.emptyList()))
 			.withMessageContaining("'accessManager' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void mappersMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new Dispatcher(this.accessManager, null))
 			.withMessageContaining("'mappers' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/server/HttpHeaderAccessManagerTests.java

@@ -52,6 +52,7 @@ class HttpHeaderAccessManagerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void headerNameMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpHeaderAccessManager(null, SECRET))
 			.withMessageContaining("'headerName' must not be empty");
@@ -64,6 +65,7 @@ class HttpHeaderAccessManagerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void expectedSecretMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpHeaderAccessManager(HEADER, null))
 			.withMessageContaining("'expectedSecret' must not be empty");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/server/HttpStatusHandlerTests.java

@@ -54,6 +54,7 @@ class HttpStatusHandlerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void statusMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpStatusHandler(null))
 			.withMessageContaining("'status' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/remote/server/UrlHandlerMapperTests.java

@@ -38,6 +38,7 @@ class UrlHandlerMapperTests {
 	private final Handler handler = mock(Handler.class);
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void requestUriMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new UrlHandlerMapper(null, this.handler))
 			.withMessageContaining("'url' must not be empty");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/ChangeableUrlsTests.java

@@ -43,6 +43,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 class ChangeableUrlsTests {
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	File tempDir;
 
 	@Test

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/MainMethodTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.devtools.restart;
 
 import java.lang.reflect.Method;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -45,6 +46,7 @@ class MainMethodTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void threadMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new MainMethod(null))
 			.withMessageContaining("'thread' must not be null");
@@ -90,9 +92,9 @@ class MainMethodTests {
 
 		private final Runnable runnable;
 
-		private Exception exception;
+		private @Nullable Exception exception;
 
-		private MainMethod mainMethod;
+		private @Nullable MainMethod mainMethod;
 
 		TestThread(Runnable runnable) {
 			this.runnable = runnable;
@@ -104,7 +106,9 @@ class MainMethodTests {
 			if (this.exception != null) {
 				ReflectionUtils.rethrowRuntimeException(this.exception);
 			}
-			return this.mainMethod;
+			MainMethod mainMethod = this.mainMethod;
+			assertThat(mainMethod).isNotNull();
+			return mainMethod;
 		}
 
 		@Override

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/RestartScopeInitializerTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.devtools.restart;
 
 import java.util.concurrent.atomic.AtomicInteger;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.SpringApplication;
@@ -37,9 +38,9 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 class RestartScopeInitializerTests {
 
-	private static AtomicInteger createCount;
+	private static @Nullable AtomicInteger createCount;
 
-	private static AtomicInteger refreshCount;
+	private static @Nullable AtomicInteger refreshCount;
 
 	@Test
 	void restartScope() {
@@ -73,11 +74,13 @@ class RestartScopeInitializerTests {
 	static class ScopeTestBean implements ApplicationListener<ContextRefreshedEvent> {
 
 		ScopeTestBean() {
+			assertThat(createCount).isNotNull();
 			createCount.incrementAndGet();
 		}
 
 		@Override
 		public void onApplicationEvent(ContextRefreshedEvent event) {
+			assertThat(refreshCount).isNotNull();
 			refreshCount.incrementAndGet();
 		}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/RestarterTests.java

@@ -26,6 +26,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.assertj.core.api.InstanceOfAssertFactories;
 import org.awaitility.Awaitility;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -111,6 +112,7 @@ class RestarterTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void addUrlsMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> Restarter.getInstance().addUrls(null))
 			.withMessageContaining("'urls' must not be null");
@@ -124,10 +126,12 @@ class RestarterTests {
 		restarter.addUrls(urls);
 		restarter.restart();
 		ClassLoader classLoader = ((TestableRestarter) restarter).getRelaunchClassLoader();
+		assertThat(classLoader).isNotNull();
 		assertThat(((URLClassLoader) classLoader).getURLs()[0]).isEqualTo(url);
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void addClassLoaderFilesMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> Restarter.getInstance().addClassLoaderFiles(null))
 			.withMessageContaining("'classLoaderFiles' must not be null");
@@ -141,6 +145,7 @@ class RestarterTests {
 		restarter.addClassLoaderFiles(classLoaderFiles);
 		restarter.restart();
 		ClassLoader classLoader = ((TestableRestarter) restarter).getRelaunchClassLoader();
+		assertThat(classLoader).isNotNull();
 		assertThat(classLoader.getResourceAsStream("f")).hasContent("abc");
 	}
 
@@ -239,7 +244,7 @@ class RestarterTests {
 
 	static class TestableRestarter extends Restarter {
 
-		private ClassLoader relaunchClassLoader;
+		private @Nullable ClassLoader relaunchClassLoader;
 
 		TestableRestarter() {
 			this(Thread.currentThread(), new String[] {}, false, new MockRestartInitializer());
@@ -262,7 +267,7 @@ class RestarterTests {
 		}
 
 		@Override
-		protected Throwable relaunch(ClassLoader classLoader) {
+		protected @Nullable Throwable relaunch(ClassLoader classLoader) {
 			this.relaunchClassLoader = classLoader;
 			return null;
 		}
@@ -271,7 +276,7 @@ class RestarterTests {
 		protected void stop() {
 		}
 
-		ClassLoader getRelaunchClassLoader() {
+		@Nullable ClassLoader getRelaunchClassLoader() {
 			return this.relaunchClassLoader;
 		}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/SilentExitExceptionHandlerTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.devtools.restart;
 
 import java.util.concurrent.CountDownLatch;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -55,7 +56,9 @@ class SilentExitExceptionHandlerTests {
 		};
 		SilentExitExceptionHandler.setup(testThread);
 		testThread.startAndJoin();
-		assertThat(testThread.getThrown().getMessage()).isEqualTo("Expected");
+		Throwable thrown = testThread.getThrown();
+		assertThat(thrown).isNotNull();
+		assertThat(thrown.getMessage()).isEqualTo("Expected");
 	}
 
 	@Test
@@ -78,13 +81,13 @@ class SilentExitExceptionHandlerTests {
 
 	static class TestThread extends Thread {
 
-		private Throwable thrown;
+		private @Nullable Throwable thrown;
 
 		TestThread() {
 			setUncaughtExceptionHandler((thread, exception) -> TestThread.this.thrown = exception);
 		}
 
-		Throwable getThrown() {
+		@Nullable Throwable getThrown() {
 			return this.thrown;
 		}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/classloader/ClassLoaderFileTests.java

@@ -33,24 +33,28 @@ class ClassLoaderFileTests {
 	public static final byte[] BYTES = "ABC".getBytes();
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void kindMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassLoaderFile(null, null))
 			.withMessageContaining("'kind' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void addedContentsMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassLoaderFile(Kind.ADDED, null))
 			.withMessageContaining("'contents' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void modifiedContentsMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassLoaderFile(Kind.MODIFIED, null))
 			.withMessageContaining("'contents' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void deletedContentsMustBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassLoaderFile(Kind.DELETED, new byte[10]))
 			.withMessageContaining("'contents' must be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/classloader/ClassLoaderFilesTests.java

@@ -41,12 +41,14 @@ class ClassLoaderFilesTests {
 	private final ClassLoaderFiles files = new ClassLoaderFiles();
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void addFileNameMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> this.files.addFile(null, mock(ClassLoaderFile.class)))
 			.withMessageContaining("'name' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void addFileFileMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> this.files.addFile("test", null))
 			.withMessageContaining("'file' must not be null");
@@ -151,6 +153,7 @@ class ClassLoaderFilesTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void classLoaderFilesMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new ClassLoaderFiles(null))
 			.withMessageContaining("'classLoaderFiles' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/classloader/RestartClassLoaderTests.java

@@ -102,12 +102,14 @@ class RestartClassLoaderTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void parentMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new RestartClassLoader(null, new URL[] {}))
 			.withMessageContaining("'parent' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void updatedFilesMustNotBeNull() {
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new RestartClassLoader(this.parentClassLoader, new URL[] {}, null))
@@ -164,6 +166,7 @@ class RestartClassLoaderTests {
 		byte[] bytes = "abc".getBytes();
 		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.MODIFIED, bytes));
 		URL resource = this.reloadClassLoader.getResource(name);
+		assertThat(resource).isNotNull();
 		assertThat(FileCopyUtils.copyToByteArray(resource.openStream())).isEqualTo(bytes);
 	}
 

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/server/HttpRestartServerHandlerTests.java

@@ -33,6 +33,7 @@ import static org.mockito.Mockito.mock;
 class HttpRestartServerHandlerTests {
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void serverMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpRestartServerHandler(null))
 			.withMessageContaining("'server' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/server/HttpRestartServerTests.java

@@ -48,6 +48,7 @@ import static org.mockito.BDDMockito.then;
 class HttpRestartServerTests {
 
 	@Mock
+	@SuppressWarnings("NullAway.Init")
 	private RestartServer delegate;
 
 	private HttpRestartServer server;
@@ -58,12 +59,14 @@ class HttpRestartServerTests {
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void sourceDirectoryUrlFilterMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpRestartServer((SourceDirectoryUrlFilter) null))
 			.withMessageContaining("'sourceDirectoryUrlFilter' must not be null");
 	}
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void restartServerMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new HttpRestartServer((RestartServer) null))
 			.withMessageContaining("'restartServer' must not be null");

module/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/server/RestartServerTests.java

@@ -24,6 +24,7 @@ import java.util.Arrays;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
@@ -43,6 +44,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
 class RestartServerTests {
 
 	@Test
+	@SuppressWarnings("NullAway") // Test null check
 	void sourceDirectoryUrlFilterMustNotBeNull() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new RestartServer((SourceDirectoryUrlFilter) null))
 			.withMessageContaining("'sourceDirectoryUrlFilter' must not be null");
@@ -110,9 +112,9 @@ class RestartServerTests {
 			super(sourceDirectoryUrlFilter, classLoader);
 		}
 
-		private Set<URL> restartUrls;
+		private @Nullable Set<URL> restartUrls;
 
-		private ClassLoaderFiles restartFiles;
+		private @Nullable ClassLoaderFiles restartFiles;
 
 		@Override
 		protected void restart(Set<URL> urls, ClassLoaderFiles files) {