Improve null-safety of module/spring-boot-webflux

See gh-46926

Author: mhalbritter

module/spring-boot-webflux/src/main/java/org/springframework/boot/webflux/autoconfigure/error/AbstractErrorWebExceptionHandler.java

@@ -127,7 +127,7 @@ public void setViewResolvers(List<ViewResolver> viewResolvers) {
 	 * @param options options to control error attributes
 	 * @return the error attributes as a Map
 	 */
-	protected Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
+	protected Map<String, @Nullable Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
 		return this.errorAttributes.getErrorAttributes(request, options);
 	}
 
@@ -194,7 +194,7 @@ private boolean getBooleanParameter(ServerRequest request, String parameterName)
 	 * @return a Publisher of the {@link ServerResponse}
 	 */
 	protected Mono<ServerResponse> renderErrorView(String viewName, ServerResponse.BodyBuilder responseBody,
-			Map<String, Object> error) {
+			Map<String, @Nullable Object> error) {
 		if (isTemplateAvailable(viewName)) {
 			return responseBody.render(viewName, error);
 		}
@@ -234,7 +234,7 @@ private boolean isTemplateAvailable(String viewName) {
 	 * @return a Publisher of the {@link ServerResponse}
 	 */
 	protected Mono<ServerResponse> renderDefaultErrorView(ServerResponse.BodyBuilder responseBody,
-			Map<String, Object> error) {
+			Map<String, @Nullable Object> error) {
 		StringBuilder builder = new StringBuilder();
 		Date timestamp = (Date) error.get("timestamp");
 		Object message = error.get("message");

module/spring-boot-webflux/src/main/java/org/springframework/boot/webflux/autoconfigure/error/DefaultErrorWebExceptionHandler.java

@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -123,7 +124,7 @@ protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes erro
 	 * @return a {@code Publisher} of the HTTP response
 	 */
 	protected Mono<ServerResponse> renderErrorView(ServerRequest request) {
-		Map<String, Object> errorAttributes = getErrorAttributes(request, MediaType.TEXT_HTML);
+		Map<String, @Nullable Object> errorAttributes = getErrorAttributes(request, MediaType.TEXT_HTML);
 		int status = getHttpStatus(request, errorAttributes);
 		ServerResponse.BodyBuilder responseBody = ServerResponse.status(status).contentType(TEXT_HTML_UTF8);
 		return Flux.just(getData(status).toArray(new String[] {}))
@@ -150,14 +151,14 @@ private List<String> getData(int errorStatus) {
 	 * @return a {@code Publisher} of the HTTP response
 	 */
 	protected Mono<ServerResponse> renderErrorResponse(ServerRequest request) {
-		Map<String, Object> errorAttributes = getErrorAttributes(request, MediaType.ALL);
+		Map<String, @Nullable Object> errorAttributes = getErrorAttributes(request, MediaType.ALL);
 		int status = getHttpStatus(request, errorAttributes);
 		return ServerResponse.status(status)
 			.contentType(MediaType.APPLICATION_JSON)
 			.body(BodyInserters.fromValue(errorAttributes));
 	}
 
-	private Map<String, Object> getErrorAttributes(ServerRequest request, MediaType mediaType) {
+	private Map<String, @Nullable Object> getErrorAttributes(ServerRequest request, MediaType mediaType) {
 		return getErrorAttributes(request, getErrorAttributeOptions(request, mediaType));
 	}
 
@@ -235,7 +236,7 @@ protected boolean isIncludePath(ServerRequest request, MediaType produces) {
 		};
 	}
 
-	private int getHttpStatus(ServerRequest request, Map<String, Object> errorAttributes) {
+	private int getHttpStatus(ServerRequest request, Map<String, @Nullable Object> errorAttributes) {
 		return getHttpStatus(errorAttributes.containsKey("status") ? errorAttributes
 				: defaultErrorAttributes.getErrorAttributes(request, ONLY_STATUS));
 	}
@@ -245,7 +246,7 @@ private int getHttpStatus(ServerRequest request, Map<String, Object> errorAttrib
 	 * @param errorAttributes the current error information
 	 * @return the error HTTP status
 	 */
-	protected int getHttpStatus(Map<String, Object> errorAttributes) {
+	protected int getHttpStatus(Map<String, @Nullable Object> errorAttributes) {
 		Object status = errorAttributes.get("status");
 		Assert.state(status instanceof Integer, "ErrorAttributes must contain a status integer");
 		return (int) status;

module/spring-boot-webflux/src/main/java/org/springframework/boot/webflux/error/DefaultErrorAttributes.java

@@ -23,6 +23,8 @@
 import java.util.Map;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.web.error.Error;
 import org.springframework.boot.web.error.ErrorAttributeOptions;
 import org.springframework.boot.web.error.ErrorAttributeOptions.Include;
@@ -71,14 +73,15 @@ public class DefaultErrorAttributes implements ErrorAttributes {
 	private static final String ERROR_INTERNAL_ATTRIBUTE = DefaultErrorAttributes.class.getName() + ".ERROR";
 
 	@Override
-	public Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
-		Map<String, Object> errorAttributes = getErrorAttributes(request, options.isIncluded(Include.STACK_TRACE));
+	public Map<String, @Nullable Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
+		Map<String, @Nullable Object> errorAttributes = getErrorAttributes(request,
+				options.isIncluded(Include.STACK_TRACE));
 		options.retainIncluded(errorAttributes);
 		return errorAttributes;
 	}
 
-	private Map<String, Object> getErrorAttributes(ServerRequest request, boolean includeStackTrace) {
-		Map<String, Object> errorAttributes = new LinkedHashMap<>();
+	private Map<String, @Nullable Object> getErrorAttributes(ServerRequest request, boolean includeStackTrace) {
+		Map<String, @Nullable Object> errorAttributes = new LinkedHashMap<>();
 		errorAttributes.put("timestamp", new Date());
 		errorAttributes.put("path", request.requestPath().value());
 		Throwable error = getError(request);
@@ -103,14 +106,14 @@ private HttpStatus determineHttpStatus(Throwable error, MergedAnnotation<Respons
 		return responseStatusAnnotation.getValue("code", HttpStatus.class).orElse(HttpStatus.INTERNAL_SERVER_ERROR);
 	}
 
-	private void addStackTrace(Map<String, Object> errorAttributes, Throwable error) {
+	private void addStackTrace(Map<String, @Nullable Object> errorAttributes, Throwable error) {
 		StringWriter stackTrace = new StringWriter();
 		error.printStackTrace(new PrintWriter(stackTrace));
 		stackTrace.flush();
 		errorAttributes.put("trace", stackTrace.toString());
 	}
 
-	private void handleException(Map<String, Object> errorAttributes, Throwable error,
+	private void handleException(Map<String, @Nullable Object> errorAttributes, Throwable error,
 			MergedAnnotation<ResponseStatus> responseStatusAnnotation, boolean includeStackTrace) {
 		Throwable exception;
 		if (error instanceof BindingResult bindingResult) {

module/spring-boot-webflux/src/main/java/org/springframework/boot/webflux/error/ErrorAttributes.java

@@ -43,7 +43,7 @@ public interface ErrorAttributes {
 	 * @param options options for error attribute contents
 	 * @return a map of error attributes
 	 */
-	default Map<String, Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
+	default Map<String, @Nullable Object> getErrorAttributes(ServerRequest request, ErrorAttributeOptions options) {
 		return Collections.emptyMap();
 	}