diff --git a/core/spring-boot-test/src/main/java/org/springframework/boot/test/util/TestPropertyValues.java b/core/spring-boot-test/src/main/java/org/springframework/boot/test/util/TestPropertyValues.java
index 3c435bc411d..190b05ffb31 100644
--- a/core/spring-boot-test/src/main/java/org/springframework/boot/test/util/TestPropertyValues.java
+++ b/core/spring-boot-test/src/main/java/org/springframework/boot/test/util/TestPropertyValues.java
@@ -186,7 +186,7 @@ public final class TestPropertyValues {
 	 * @param call the call to make
 	 * @return the result of the call
 	 */
-	public <T> T applyToSystemProperties(Callable<T> call) {
+	public <T extends @Nullable Object> T applyToSystemProperties(Callable<T> call) {
 		try (SystemPropertiesHandler handler = new SystemPropertiesHandler()) {
 			return call.call();
 		}
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/EndpointMBean.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/EndpointMBean.java
index 21e983a96fd..38f213d296c 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/EndpointMBean.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/EndpointMBean.java
@@ -55,7 +55,7 @@ public class EndpointMBean implements DynamicMBean {
 
 	private final JmxOperationResponseMapper responseMapper;
 
-	private final ClassLoader classLoader;
+	private final @Nullable ClassLoader classLoader;
 
 	private final ExposableJmxEndpoint endpoint;
 
@@ -63,7 +63,8 @@ public class EndpointMBean implements DynamicMBean {
 
 	private final Map<String, JmxOperation> operations;
 
-	EndpointMBean(JmxOperationResponseMapper responseMapper, ClassLoader classLoader, ExposableJmxEndpoint endpoint) {
+	EndpointMBean(JmxOperationResponseMapper responseMapper, @Nullable ClassLoader classLoader,
+			ExposableJmxEndpoint endpoint) {
 		Assert.notNull(responseMapper, "'responseMapper' must not be null");
 		Assert.notNull(endpoint, "'endpoint' must not be null");
 		this.responseMapper = responseMapper;
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JacksonJmxOperationResponseMapper.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JacksonJmxOperationResponseMapper.java
index ef074123d1d..986b8da05a1 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JacksonJmxOperationResponseMapper.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JacksonJmxOperationResponseMapper.java
@@ -24,6 +24,8 @@ import org.jspecify.annotations.Nullable;
 import tools.jackson.databind.JavaType;
 import tools.jackson.databind.ObjectMapper;
 
+import org.springframework.lang.Contract;
+
 /**
  * {@link JmxOperationResponseMapper} that delegates to a Jackson {@link ObjectMapper} to
  * return a JSON response.
@@ -58,6 +60,7 @@ public class JacksonJmxOperationResponseMapper implements JmxOperationResponseMa
 	}
 
 	@Override
+	@Contract("!null -> !null")
 	public @Nullable Object mapResponse(@Nullable Object response) {
 		if (response == null) {
 			return null;
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/ServletEndpointRegistrar.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/ServletEndpointRegistrar.java
index c0f82855790..b6a8c3f075b 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/ServletEndpointRegistrar.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/ServletEndpointRegistrar.java
@@ -65,11 +65,11 @@ public class ServletEndpointRegistrar implements ServletContextInitializer {
 
 	private final EndpointAccessResolver endpointAccessResolver;
 
-	public ServletEndpointRegistrar(String basePath, Collection<ExposableServletEndpoint> servletEndpoints) {
+	public ServletEndpointRegistrar(@Nullable String basePath, Collection<ExposableServletEndpoint> servletEndpoints) {
 		this(basePath, servletEndpoints, (endpointId, defaultAccess) -> Access.NONE);
 	}
 
-	public ServletEndpointRegistrar(String basePath, Collection<ExposableServletEndpoint> servletEndpoints,
+	public ServletEndpointRegistrar(@Nullable String basePath, Collection<ExposableServletEndpoint> servletEndpoints,
 			EndpointAccessResolver endpointAccessResolver) {
 		Assert.notNull(servletEndpoints, "'servletEndpoints' must not be null");
 		this.basePath = cleanBasePath(basePath);
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointDiscoverer.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointDiscoverer.java
index d519abd2f9b..57cb5687c19 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointDiscoverer.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointDiscoverer.java
@@ -53,7 +53,7 @@ import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
 public class ControllerEndpointDiscoverer extends EndpointDiscoverer<ExposableControllerEndpoint, Operation>
 		implements ControllerEndpointsSupplier {
 
-	private final List<PathMapper> endpointPathMappers;
+	private final @Nullable List<PathMapper> endpointPathMappers;
 
 	/**
 	 * Create a new {@link ControllerEndpointDiscoverer} instance.
@@ -61,7 +61,8 @@ public class ControllerEndpointDiscoverer extends EndpointDiscoverer<ExposableCo
 	 * @param endpointPathMappers the endpoint path mappers
 	 * @param filters filters to apply
 	 */
-	public ControllerEndpointDiscoverer(ApplicationContext applicationContext, List<PathMapper> endpointPathMappers,
+	public ControllerEndpointDiscoverer(ApplicationContext applicationContext,
+			@Nullable List<PathMapper> endpointPathMappers,
 			Collection<EndpointFilter<ExposableControllerEndpoint>> filters) {
 		super(applicationContext, ParameterValueMapper.NONE, Collections.emptyList(), filters, Collections.emptyList());
 		this.endpointPathMappers = endpointPathMappers;
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ServletEndpointDiscoverer.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ServletEndpointDiscoverer.java
index 53349220c3e..72d1ef6be50 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ServletEndpointDiscoverer.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ServletEndpointDiscoverer.java
@@ -53,7 +53,7 @@ import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
 public class ServletEndpointDiscoverer extends EndpointDiscoverer<ExposableServletEndpoint, Operation>
 		implements ServletEndpointsSupplier {
 
-	private final List<PathMapper> endpointPathMappers;
+	private final @Nullable List<PathMapper> endpointPathMappers;
 
 	/**
 	 * Create a new {@link ServletEndpointDiscoverer} instance.
@@ -61,7 +61,8 @@ public class ServletEndpointDiscoverer extends EndpointDiscoverer<ExposableServl
 	 * @param endpointPathMappers the endpoint path mappers
 	 * @param filters filters to apply
 	 */
-	public ServletEndpointDiscoverer(ApplicationContext applicationContext, List<PathMapper> endpointPathMappers,
+	public ServletEndpointDiscoverer(ApplicationContext applicationContext,
+			@Nullable List<PathMapper> endpointPathMappers,
 			Collection<EndpointFilter<ExposableServletEndpoint>> filters) {
 		super(applicationContext, ParameterValueMapper.NONE, Collections.emptyList(), filters, Collections.emptyList());
 		this.endpointPathMappers = endpointPathMappers;
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/HealthEndpoint.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/HealthEndpoint.java
index d08cec6c4ae..07763085b07 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/HealthEndpoint.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/HealthEndpoint.java
@@ -62,7 +62,7 @@ public class HealthEndpoint extends HealthEndpointSupport<Health, HealthDescript
 	 */
 	public HealthEndpoint(HealthContributorRegistry registry,
 			@Nullable ReactiveHealthContributorRegistry fallbackRegistry, HealthEndpointGroups groups,
-			Duration slowContributorLoggingThreshold) {
+			@Nullable Duration slowContributorLoggingThreshold) {
 		super(Contributor.blocking(registry, fallbackRegistry), groups, slowContributorLoggingThreshold);
 	}
 
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/ReactiveHealthEndpointWebExtension.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/ReactiveHealthEndpointWebExtension.java
index fd4ff9317de..a5a65556800 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/ReactiveHealthEndpointWebExtension.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/ReactiveHealthEndpointWebExtension.java
@@ -69,13 +69,13 @@ public class ReactiveHealthEndpointWebExtension
 
 	@ReadOperation
 	public Mono<WebEndpointResponse<? extends HealthDescriptor>> health(ApiVersion apiVersion,
-			WebServerNamespace serverNamespace, SecurityContext securityContext) {
+			@Nullable WebServerNamespace serverNamespace, SecurityContext securityContext) {
 		return health(apiVersion, serverNamespace, securityContext, false, EMPTY_PATH);
 	}
 
 	@ReadOperation
 	public Mono<WebEndpointResponse<? extends HealthDescriptor>> health(ApiVersion apiVersion,
-			WebServerNamespace serverNamespace, SecurityContext securityContext,
+			@Nullable WebServerNamespace serverNamespace, SecurityContext securityContext,
 			@Selector(match = Match.ALL_REMAINING) String... path) {
 		return health(apiVersion, serverNamespace, securityContext, false, path);
 	}
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SystemHealthDescriptor.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SystemHealthDescriptor.java
index 50e62c9e13e..8eca392e759 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SystemHealthDescriptor.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SystemHealthDescriptor.java
@@ -34,16 +34,16 @@ import org.springframework.boot.health.contributor.Status;
  */
 public final class SystemHealthDescriptor extends CompositeHealthDescriptor {
 
-	private final Set<String> groups;
+	private final @Nullable Set<String> groups;
 
 	SystemHealthDescriptor(ApiVersion apiVersion, Status status, @Nullable Map<String, HealthDescriptor> components,
-			Set<String> groups) {
+			@Nullable Set<String> groups) {
 		super(apiVersion, status, components);
 		this.groups = groups;
 	}
 
 	@JsonInclude(Include.NON_EMPTY)
-	public Set<String> getGroups() {
+	public @Nullable Set<String> getGroups() {
 		return this.groups;
 	}