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

See gh-47263

module/spring-boot-webflux/build.gradle

@@ -58,3 +58,7 @@ dependencies {
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 	testRuntimeOnly("jakarta.servlet:jakarta.servlet-api")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/actuate/endpoint/web/ControllerEndpointHandlerMappingTests.java

@@ -16,9 +16,11 @@
 
 package org.springframework.boot.webflux.actuate.endpoint.web;
 
+import java.lang.reflect.Method;
 import java.time.Duration;
 import java.util.Arrays;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.actuate.endpoint.Access;
@@ -96,7 +98,8 @@ class ControllerEndpointHandlerMappingTests {
 			.isThrownBy(() -> getHandler(mapping, HttpMethod.POST, "/actuator/first"));
 	}
 
-	private Object getHandler(ControllerEndpointHandlerMapping mapping, HttpMethod method, String requestURI) {
+	private @Nullable Object getHandler(ControllerEndpointHandlerMapping mapping, HttpMethod method,
+			String requestURI) {
 		return mapping.getHandler(exchange(method, requestURI)).block(Duration.ofSeconds(30));
 	}
 
@@ -109,7 +112,9 @@ class ControllerEndpointHandlerMappingTests {
 	}
 
 	private HandlerMethod handlerOf(Object source, String methodName) {
-		return new HandlerMethod(source, ReflectionUtils.findMethod(source.getClass(), methodName));
+		Method method = ReflectionUtils.findMethod(source.getClass(), methodName);
+		assertThat(method).isNotNull();
+		return new HandlerMethod(source, method);
 	}
 
 	private MockServerWebExchange exchange(HttpMethod method, String requestURI) {

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/HttpHandlerAutoConfigurationTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.webflux.autoconfigure;
 
 import org.assertj.core.api.InstanceOfAssertFactories;
 import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
@@ -104,12 +105,12 @@ class HttpHandlerAutoConfigurationTests {
 
 		@Bean
 		HttpHandler customHttpHandler() {
-			return (serverHttpRequest, serverHttpResponse) -> null;
+			return (serverHttpRequest, serverHttpResponse) -> Mono.empty();
 		}
 
 		@Bean
 		RouterFunction<ServerResponse> routerFunction() {
-			return route(GET("/test"), (serverRequest) -> null);
+			return route(GET("/test"), (serverRequest) -> Mono.empty());
 		}
 
 	}

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/WebFluxAutoConfigurationTests.java

@@ -38,11 +38,13 @@ import org.aspectj.lang.annotation.AfterReturning;
 import org.aspectj.lang.annotation.Aspect;
 import org.assertj.core.api.Assertions;
 import org.assertj.core.api.InstanceOfAssertFactories;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.EnabledForJreRange;
 import org.junit.jupiter.api.condition.JRE;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
+import reactor.core.publisher.Mono;
 
 import org.springframework.aop.support.AopUtils;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
@@ -109,6 +111,7 @@ import org.springframework.web.reactive.resource.CachingResourceTransformer;
 import org.springframework.web.reactive.resource.PathResourceResolver;
 import org.springframework.web.reactive.resource.ResourceWebHandler;
 import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolver;
+import org.springframework.web.reactive.result.method.annotation.ArgumentResolverConfigurer;
 import org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerAdapter;
 import org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerMapping;
 import org.springframework.web.reactive.result.method.annotation.ResponseEntityExceptionHandler;
@@ -178,8 +181,10 @@ class WebFluxAutoConfigurationTests {
 	void shouldRegisterCustomHandlerMethodArgumentResolver() {
 		this.contextRunner.withUserConfiguration(CustomArgumentResolvers.class).run((context) -> {
 			RequestMappingHandlerAdapter adapter = context.getBean(RequestMappingHandlerAdapter.class);
+			ArgumentResolverConfigurer configurer = adapter.getArgumentResolverConfigurer();
+			assertThat(configurer).isNotNull();
 			List<HandlerMethodArgumentResolver> customResolvers = (List<HandlerMethodArgumentResolver>) ReflectionTestUtils
-				.getField(adapter.getArgumentResolverConfigurer(), "customResolvers");
+				.getField(configurer, "customResolvers");
 			assertThat(customResolvers).contains(context.getBean("firstResolver", HandlerMethodArgumentResolver.class),
 					context.getBean("secondResolver", HandlerMethodArgumentResolver.class));
 		});
@@ -564,9 +569,9 @@ class WebFluxAutoConfigurationTests {
 	void whenFixedLocalContextResolverIsUsedThenAcceptLanguagesHeaderIsIgnored() {
 		this.contextRunner.withPropertyValues("spring.web.locale:en_UK", "spring.web.locale-resolver=fixed")
 			.run((context) -> {
-				MockServerHttpRequest request = MockServerHttpRequest.get("/")
+				Locale locale = StringUtils.parseLocaleString("nl_NL");
-					.acceptLanguageAsLocales(StringUtils.parseLocaleString("nl_NL"))
+				assertThat(locale).isNotNull();
-					.build();
+				MockServerHttpRequest request = MockServerHttpRequest.get("/").acceptLanguageAsLocales(locale).build();
 				MockServerWebExchange exchange = MockServerWebExchange.from(request);
 				LocaleContextResolver localeContextResolver = context.getBean(LocaleContextResolver.class);
 				assertThat(localeContextResolver).isInstanceOf(FixedLocaleContextResolver.class);
@@ -578,14 +583,14 @@ class WebFluxAutoConfigurationTests {
 	@Test
 	void whenAcceptHeaderLocaleContextResolverIsUsedThenAcceptLanguagesHeaderIsHonoured() {
 		this.contextRunner.withPropertyValues("spring.web.locale:en_UK").run((context) -> {
-			MockServerHttpRequest request = MockServerHttpRequest.get("/")
+			Locale locale = StringUtils.parseLocaleString("nl_NL");
-				.acceptLanguageAsLocales(StringUtils.parseLocaleString("nl_NL"))
+			assertThat(locale).isNotNull();
-				.build();
+			MockServerHttpRequest request = MockServerHttpRequest.get("/").acceptLanguageAsLocales(locale).build();
 			MockServerWebExchange exchange = MockServerWebExchange.from(request);
 			LocaleContextResolver localeContextResolver = context.getBean(LocaleContextResolver.class);
 			assertThat(localeContextResolver).isInstanceOf(AcceptHeaderLocaleContextResolver.class);
 			LocaleContext localeContext = localeContextResolver.resolveLocaleContext(exchange);
-			assertThat(localeContext.getLocale()).isEqualTo(StringUtils.parseLocaleString("nl_NL"));
+			assertThat(localeContext.getLocale()).isEqualTo(locale);
 		});
 	}
 
@@ -674,12 +679,15 @@ class WebFluxAutoConfigurationTests {
 			.run(assertExchangeWithSession((exchange) -> {
 				List<ResponseCookie> cookies = exchange.getResponse().getCookies().get("JSESSIONID");
 				assertThat(cookies).isNotEmpty();
-				assertThat(cookies).allMatch((cookie) -> cookie.getDomain().equals(".example.com"));
+				assertThat(cookies)
-				assertThat(cookies).allMatch((cookie) -> cookie.getPath().equals("/example"));
+					.allMatch((cookie) -> cookie.getDomain() != null && cookie.getDomain().equals(".example.com"));
+				assertThat(cookies)
+					.allMatch((cookie) -> cookie.getPath() != null && cookie.getPath().equals("/example"));
 				assertThat(cookies).allMatch((cookie) -> cookie.getMaxAge().equals(Duration.ofSeconds(60)));
 				assertThat(cookies).allMatch((cookie) -> !cookie.isHttpOnly());
 				assertThat(cookies).allMatch((cookie) -> !cookie.isSecure());
-				assertThat(cookies).allMatch((cookie) -> cookie.getSameSite().equals("Strict"));
+				assertThat(cookies)
+					.allMatch((cookie) -> cookie.getSameSite() != null && cookie.getSameSite().equals("Strict"));
 				assertThat(cookies).allMatch(ResponseCookie::isPartitioned);
 			}));
 	}
@@ -906,6 +914,7 @@ class WebFluxAutoConfigurationTests {
 			MockServerWebExchange webExchange = MockServerWebExchange.from(request);
 			WebSessionManager webSessionManager = context.getBean(WebSessionManager.class);
 			WebSession webSession = webSessionManager.getSession(webExchange).block();
+			assertThat(webSession).isNotNull();
 			webSession.start();
 			webExchange.getResponse().setComplete().block();
 			exchange.accept(webExchange);
@@ -1024,7 +1033,7 @@ class WebFluxAutoConfigurationTests {
 
 		@Bean
 		HttpHandler httpHandler() {
-			return (serverHttpRequest, serverHttpResponse) -> null;
+			return (serverHttpRequest, serverHttpResponse) -> Mono.empty();
 		}
 
 	}
@@ -1198,7 +1207,7 @@ class WebFluxAutoConfigurationTests {
 		}
 
 		@Override
-		public void setLocaleContext(ServerWebExchange exchange, LocaleContext localeContext) {
+		public void setLocaleContext(ServerWebExchange exchange, @Nullable LocaleContext localeContext) {
 		}
 
 	}

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/WelcomePageRouterFunctionFactoryTests.java

@@ -21,6 +21,7 @@ import java.util.Collections;
 import java.util.Locale;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import reactor.core.publisher.Mono;
@@ -36,6 +37,8 @@ import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.web.reactive.function.server.HandlerStrategies;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.ServerResponse;
 import org.springframework.web.reactive.result.view.View;
 import org.springframework.web.reactive.result.view.ViewResolver;
 import org.springframework.web.server.ServerWebExchange;
@@ -166,13 +169,17 @@ class WelcomePageRouterFunctionFactoryTests {
 
 	private WebTestClient withStaticIndex() {
 		WelcomePageRouterFunctionFactory factory = factoryWithoutTemplateSupport(this.indexLocations, "/**");
-		return WebTestClient.bindToRouterFunction(factory.createRouterFunction()).build();
+		RouterFunction<ServerResponse> routerFunction = factory.createRouterFunction();
+		assertThat(routerFunction).isNotNull();
+		return WebTestClient.bindToRouterFunction(routerFunction).build();
 	}
 
 	private WebTestClient withTemplateIndex() {
 		WelcomePageRouterFunctionFactory factory = factoryWithTemplateSupport(this.noIndexLocations);
 		TestViewResolver testViewResolver = new TestViewResolver();
-		return WebTestClient.bindToRouterFunction(factory.createRouterFunction())
+		RouterFunction<ServerResponse> routerFunction = factory.createRouterFunction();
+		assertThat(routerFunction).isNotNull();
+		return WebTestClient.bindToRouterFunction(routerFunction)
 			.handlerStrategies(HandlerStrategies.builder().viewResolver(testViewResolver).build())
 			.build();
 	}
@@ -180,7 +187,9 @@ class WelcomePageRouterFunctionFactoryTests {
 	private WebTestClient withStaticAndTemplateIndex() {
 		WelcomePageRouterFunctionFactory factory = factoryWithTemplateSupport(this.indexLocations);
 		TestViewResolver testViewResolver = new TestViewResolver();
-		return WebTestClient.bindToRouterFunction(factory.createRouterFunction())
+		RouterFunction<ServerResponse> routerFunction = factory.createRouterFunction();
+		assertThat(routerFunction).isNotNull();
+		return WebTestClient.bindToRouterFunction(routerFunction)
 			.handlerStrategies(HandlerStrategies.builder().viewResolver(testViewResolver).build())
 			.build();
 	}
@@ -226,7 +235,8 @@ class WelcomePageRouterFunctionFactoryTests {
 		private final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();
 
 		@Override
-		public Mono<Void> render(Map<String, ?> model, MediaType contentType, ServerWebExchange exchange) {
+		public Mono<Void> render(@Nullable Map<String, ?> model, @Nullable MediaType contentType,
+				ServerWebExchange exchange) {
 			DataBuffer buffer = this.bufferFactory.wrap("welcome-page-template".getBytes(StandardCharsets.UTF_8));
 			return exchange.getResponse().writeWith(Mono.just(buffer));
 		}

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/actuate/web/ControllerEndpointWebFluxIntegrationTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.webflux.autoconfigure.actuate.web;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 
@@ -44,11 +45,13 @@ import org.springframework.web.bind.annotation.GetMapping;
 @SuppressWarnings("removal")
 class ControllerEndpointWebFluxIntegrationTests {
 
-	private AnnotationConfigReactiveWebApplicationContext context;
+	private @Nullable AnnotationConfigReactiveWebApplicationContext context;
 
 	@AfterEach
 	void close() {
-		this.context.close();
+		if (this.context != null) {
+			this.context.close();
+		}
 	}
 
 	@Test

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/actuate/web/WebFluxEndpointAccessIntegrationTests.java

@@ -30,6 +30,7 @@ import org.springframework.boot.jackson.autoconfigure.JacksonAutoConfiguration;
 import org.springframework.boot.reactor.netty.autoconfigure.NettyReactiveWebServerAutoConfiguration;
 import org.springframework.boot.test.context.assertj.AssertableReactiveWebApplicationContext;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
+import org.springframework.boot.web.server.WebServer;
 import org.springframework.boot.web.server.reactive.context.AnnotationConfigReactiveWebServerApplicationContext;
 import org.springframework.boot.web.server.reactive.context.ReactiveWebServerApplicationContext;
 import org.springframework.boot.webflux.autoconfigure.HttpHandlerAutoConfiguration;
@@ -137,9 +138,10 @@ class WebFluxEndpointAccessIntegrationTests {
 	}
 
 	private WebTestClient createClient(AssertableReactiveWebApplicationContext context) {
-		int port = context.getSourceApplicationContext(ReactiveWebServerApplicationContext.class)
+		WebServer webServer = context.getSourceApplicationContext(ReactiveWebServerApplicationContext.class)
-			.getWebServer()
+			.getWebServer();
-			.getPort();
+		assertThat(webServer).isNotNull();
+		int port = webServer.getPort();
 		ExchangeStrategies exchangeStrategies = ExchangeStrategies.builder()
 			.codecs((configurer) -> configurer.defaultCodecs().maxInMemorySize(-1))
 			.build();

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/actuate/web/WebFluxManagementChildContextConfigurationIntegrationTests.java

@@ -26,6 +26,7 @@ import java.util.function.Consumer;
 import org.apache.catalina.Valve;
 import org.apache.catalina.startup.Tomcat;
 import org.apache.catalina.valves.AccessLogValve;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
@@ -80,6 +81,7 @@ class WebFluxManagementChildContextConfigurationIntegrationTests {
 		.withPropertyValues("server.port=0", "management.server.port=0", "management.endpoints.web.exposure.include=*");
 
 	@TempDir
+	@SuppressWarnings("NullAway.Init")
 	Path temp;
 
 	@Test
@@ -122,7 +124,7 @@ class WebFluxManagementChildContextConfigurationIntegrationTests {
 		});
 	}
 
-	private AccessLogValve findAccessLogValve() {
+	private @Nullable AccessLogValve findAccessLogValve() {
 		assertThat(this.webServers).hasSize(2);
 		Tomcat tomcat = ((TomcatWebServer) this.webServers.get(1)).getTomcat();
 		for (Valve valve : tomcat.getEngine().getPipeline().getValves()) {

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/error/DefaultErrorWebExceptionHandlerIntegrationTests.java

@@ -22,6 +22,7 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 
 import jakarta.validation.Valid;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -568,7 +569,7 @@ class DefaultErrorWebExceptionHandlerIntegrationTests {
 
 	private static final class LogIdFilter implements WebFilter {
 
-		private String logId;
+		private @Nullable String logId;
 
 		@Override
 		public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
@@ -576,7 +577,7 @@ class DefaultErrorWebExceptionHandlerIntegrationTests {
 			return chain.filter(exchange);
 		}
 
-		String getLogId() {
+		@Nullable String getLogId() {
 			return this.logId;
 		}
 
@@ -627,8 +628,9 @@ class DefaultErrorWebExceptionHandlerIntegrationTests {
 		ErrorAttributes errorAttributes() {
 			return new DefaultErrorAttributes() {
 				@Override
-				public Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
+				public Map<String, @Nullable Object> getErrorAttributes(ServerRequest request,
-					Map<String, Object> errorAttributes = super.getErrorAttributes(request, options);
+						ErrorAttributeOptions options) {
+					Map<String, @Nullable Object> errorAttributes = super.getErrorAttributes(request, options);
 					errorAttributes.put("error", "custom error");
 					errorAttributes.put("newAttribute", "value");
 					errorAttributes.remove("path");
@@ -648,8 +650,9 @@ class DefaultErrorWebExceptionHandlerIntegrationTests {
 			return new DefaultErrorAttributes() {
 
 				@Override
-				public Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
+				public Map<String, @Nullable Object> getErrorAttributes(ServerRequest request,
-					Map<String, Object> errorAttributes = new HashMap<>();
+						ErrorAttributeOptions options) {
+					Map<String, @Nullable Object> errorAttributes = new HashMap<>();
 					errorAttributes.put("status", 400);
 					errorAttributes.put("error", "custom error");
 					return errorAttributes;
@@ -693,8 +696,10 @@ class DefaultErrorWebExceptionHandlerIntegrationTests {
 			return new DefaultErrorAttributes() {
 
 				@Override
-				public Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
+				public Map<String, @Nullable Object> getErrorAttributes(ServerRequest request,
-					Map<String, Object> attributes = new LinkedHashMap<>(super.getErrorAttributes(request, options));
+						ErrorAttributeOptions options) {
+					Map<String, @Nullable Object> attributes = new LinkedHashMap<>(
+							super.getErrorAttributes(request, options));
 					attributes.remove("status");
 					return attributes;
 				}

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/autoconfigure/error/DummyBody.java

@@ -21,6 +21,7 @@ import jakarta.validation.constraints.NotNull;
 public class DummyBody {
 
 	@NotNull
+	@SuppressWarnings("NullAway.Init")
 	private String content;
 
 	public String getContent() {

module/spring-boot-webflux/src/test/java/org/springframework/boot/webflux/error/DefaultErrorAttributesTests.java

@@ -22,6 +22,7 @@ import java.util.Date;
 import java.util.List;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.web.error.ErrorAttributeOptions;
@@ -77,8 +78,8 @@ class DefaultErrorAttributesTests {
 	@Test
 	void includeTimeStamp() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, NOT_FOUND),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, NOT_FOUND), ErrorAttributeOptions.defaults());
 		assertThat(attributes.get("timestamp")).isInstanceOf(Date.class);
 	}
 
@@ -86,8 +87,8 @@ class DefaultErrorAttributesTests {
 	void defaultStatusCode() {
 		Error error = new OutOfMemoryError("Test error");
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, error),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, error), ErrorAttributeOptions.defaults());
 		assertThat(attributes).containsEntry("error", HttpStatus.INTERNAL_SERVER_ERROR.getReasonPhrase());
 		assertThat(attributes).containsEntry("status", 500);
 	}
@@ -96,8 +97,8 @@ class DefaultErrorAttributesTests {
 	void annotatedResponseStatusCode() {
 		Exception error = new CustomException();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, error),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, error), ErrorAttributeOptions.defaults());
 		assertThat(attributes).containsEntry("error", HttpStatus.EXPECTATION_FAILED.getReasonPhrase());
 		assertThat(attributes).doesNotContainKey("message");
 		assertThat(attributes).containsEntry("status", HttpStatus.EXPECTATION_FAILED.value());
@@ -107,7 +108,8 @@ class DefaultErrorAttributesTests {
 	void annotatedResponseStatusCodeWithExceptionMessage() {
 		Exception error = new CustomException("Test Message");
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, error),
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(
+				buildServerRequest(request, error),
 				ErrorAttributeOptions.of(Include.MESSAGE, Include.STATUS, Include.ERROR));
 		assertThat(attributes).containsEntry("error", HttpStatus.EXPECTATION_FAILED.getReasonPhrase());
 		assertThat(attributes).containsEntry("message", "Test Message");
@@ -118,7 +120,8 @@ class DefaultErrorAttributesTests {
 	void annotatedResponseStatusCodeWithCustomReasonPhrase() {
 		Exception error = new Custom2Exception();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, error),
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(
+				buildServerRequest(request, error),
 				ErrorAttributeOptions.of(Include.MESSAGE, Include.STATUS, Include.ERROR));
 		assertThat(attributes).containsEntry("error", HttpStatus.EXPECTATION_FAILED.getReasonPhrase());
 		assertThat(attributes).containsEntry("status", HttpStatus.EXPECTATION_FAILED.value());
@@ -128,8 +131,8 @@ class DefaultErrorAttributesTests {
 	@Test
 	void includeStatusCode() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, NOT_FOUND),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, NOT_FOUND), ErrorAttributeOptions.defaults());
 		assertThat(attributes).containsEntry("error", HttpStatus.NOT_FOUND.getReasonPhrase());
 		assertThat(attributes).containsEntry("status", 404);
 	}
@@ -139,7 +142,7 @@ class DefaultErrorAttributesTests {
 		Error error = new OutOfMemoryError("Test error");
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.of(Include.MESSAGE));
 		assertThat(this.errorAttributes.getError(serverRequest)).isSameAs(error);
 		assertThat(attributes).doesNotContainKey("exception");
@@ -151,7 +154,7 @@ class DefaultErrorAttributesTests {
 		Error error = new OutOfMemoryError("Test error");
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.defaults());
 		assertThat(this.errorAttributes.getError(serverRequest)).isSameAs(error);
 		assertThat(attributes).doesNotContainKey("message");
@@ -163,7 +166,7 @@ class DefaultErrorAttributesTests {
 		this.errorAttributes = new DefaultErrorAttributes();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.of(Include.EXCEPTION, Include.MESSAGE));
 		assertThat(this.errorAttributes.getError(serverRequest)).isSameAs(error);
 		assertThat(attributes).containsEntry("exception", RuntimeException.class.getName());
@@ -177,7 +180,7 @@ class DefaultErrorAttributesTests {
 		this.errorAttributes = new DefaultErrorAttributes();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.of(Include.EXCEPTION, Include.MESSAGE, Include.STATUS));
 		assertThat(attributes).containsEntry("status", 400);
 		assertThat(attributes).containsEntry("message", "invalid request");
@@ -192,7 +195,7 @@ class DefaultErrorAttributesTests {
 		this.errorAttributes = new DefaultErrorAttributes();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.of(Include.EXCEPTION, Include.MESSAGE, Include.STATUS));
 		assertThat(attributes).containsEntry("status", 406);
 		assertThat(attributes).containsEntry("message", "could not process request");
@@ -204,8 +207,8 @@ class DefaultErrorAttributesTests {
 	void notIncludeTrace() {
 		RuntimeException ex = new RuntimeException("Test");
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, ex),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, ex), ErrorAttributeOptions.defaults());
 		assertThat(attributes).doesNotContainKey("trace");
 	}
 
@@ -213,40 +216,42 @@ class DefaultErrorAttributesTests {
 	void includeTrace() {
 		RuntimeException ex = new RuntimeException("Test");
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, ex),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.of(Include.STACK_TRACE));
+			.getErrorAttributes(buildServerRequest(request, ex), ErrorAttributeOptions.of(Include.STACK_TRACE));
-		assertThat(attributes.get("trace").toString()).startsWith("java.lang");
+		Object trace = attributes.get("trace");
+		assertThat(trace).isNotNull();
+		assertThat(trace.toString()).startsWith("java.lang");
 	}
 
 	@Test
 	void includePathByDefault() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, NOT_FOUND),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, NOT_FOUND), ErrorAttributeOptions.defaults());
 		assertThat(attributes).containsEntry("path", "/test");
 	}
 
 	@Test
 	void includePath() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, NOT_FOUND),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.of(Include.PATH));
+			.getErrorAttributes(buildServerRequest(request, NOT_FOUND), ErrorAttributeOptions.of(Include.PATH));
 		assertThat(attributes).containsEntry("path", "/test");
 	}
 
 	@Test
 	void pathShouldIncludeContext() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/context/test").contextPath("/context").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, NOT_FOUND),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.of(Include.PATH));
+			.getErrorAttributes(buildServerRequest(request, NOT_FOUND), ErrorAttributeOptions.of(Include.PATH));
 		assertThat(attributes).containsEntry("path", "/context/test");
 	}
 
 	@Test
 	void excludePath() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, NOT_FOUND),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.of());
+			.getErrorAttributes(buildServerRequest(request, NOT_FOUND), ErrorAttributeOptions.of());
 		assertThat(attributes).doesNotContainEntry("path", "/test");
 	}
 
@@ -254,7 +259,7 @@ class DefaultErrorAttributesTests {
 	void includeLogPrefix() {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, NOT_FOUND);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.defaults());
 		assertThat(attributes).containsEntry("requestId", serverRequest.exchange().getRequest().getId());
 	}
@@ -267,8 +272,8 @@ class DefaultErrorAttributesTests {
 		bindingResult.addError(new ObjectError("c", "d"));
 		Exception ex = new WebExchangeBindException(stringParam, bindingResult);
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, ex),
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(
-				ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
+				buildServerRequest(request, ex), ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
 		assertThat(attributes.get("message")).asString()
 			.startsWith("Validation failed for argument at index 0 in method: " + "int " + getClass().getName()
 					+ ".method(java.lang.String), with 1 error(s)");
@@ -284,7 +289,7 @@ class DefaultErrorAttributesTests {
 		bindingResult.addError(new ObjectError("c", "d"));
 		Exception ex = new WebExchangeBindException(stringParam, bindingResult);
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(
 				buildServerRequest(request, new ResponseStatusException(HttpStatus.BAD_REQUEST, "Invalid", ex)),
 				ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
 		assertThat(attributes.get("message")).isEqualTo("Invalid");
@@ -305,8 +310,8 @@ class DefaultErrorAttributesTests {
 						})));
 		HandlerMethodValidationException ex = new HandlerMethodValidationException(methodValidationResult);
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, ex),
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(
-				ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
+				buildServerRequest(request, ex), ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
 		assertThat(attributes.get("message")).asString()
 			.isEqualTo(
 					"Validation failed for method='public java.lang.String java.lang.String.substring(int)'. Error count: 1");
@@ -322,8 +327,8 @@ class DefaultErrorAttributesTests {
 		bindingResult.addError(new ObjectError("c", "d"));
 		Exception ex = new WebExchangeBindException(stringParam, bindingResult);
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, ex),
+		Map<String, @Nullable Object> attributes = this.errorAttributes
-				ErrorAttributeOptions.defaults());
+			.getErrorAttributes(buildServerRequest(request, ex), ErrorAttributeOptions.defaults());
 		assertThat(attributes).doesNotContainKey("message");
 		assertThat(attributes).doesNotContainKey("errors");
 	}
@@ -342,8 +347,8 @@ class DefaultErrorAttributesTests {
 				List.of(parameterValidationResult));
 		HandlerMethodValidationException ex = new HandlerMethodValidationException(methodValidationResult);
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(buildServerRequest(request, ex),
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(
-				ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
+				buildServerRequest(request, ex), ErrorAttributeOptions.of(Include.MESSAGE, Include.BINDING_ERRORS));
 		assertThat(attributes.get("message")).asString()
 			.isEqualTo(
 					"Validation failed for method='public java.lang.String java.lang.String.substring(int)'. Error count: 1");
@@ -358,7 +363,7 @@ class DefaultErrorAttributesTests {
 		this.errorAttributes = new DefaultErrorAttributes();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.defaults().excluding(Include.STATUS));
 		assertThat(attributes).doesNotContainKey("status");
 	}
@@ -370,7 +375,7 @@ class DefaultErrorAttributesTests {
 		this.errorAttributes = new DefaultErrorAttributes();
 		MockServerHttpRequest request = MockServerHttpRequest.get("/test").build();
 		ServerRequest serverRequest = buildServerRequest(request, error);
-		Map<String, Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
+		Map<String, @Nullable Object> attributes = this.errorAttributes.getErrorAttributes(serverRequest,
 				ErrorAttributeOptions.defaults().excluding(Include.ERROR));
 		assertThat(attributes).doesNotContainKey("error");
 	}