Perform NullAway build-time checks in spring-web

Also in spring-websocket.

See spring-projectsgh-32475

gradle/spring-module.gradle

@@ -118,7 +118,7 @@ tasks.withType(JavaCompile).configureEach {
     	disableAllChecks = true
         option("NullAway:CustomContractAnnotations", "org.springframework.lang.Contract")
         option("NullAway:AnnotatedPackages", "org.springframework.core,org.springframework.expression," +
-        		"org.springframework.web.reactive,org.springframework.web.servlet")
+        		"org.springframework.web")
         option("NullAway:UnannotatedSubPackages", "org.springframework.instrument,org.springframework.context.index," +
 				"org.springframework.asm,org.springframework.cglib,org.springframework.objenesis," +
 				"org.springframework.javapoet,org.springframework.aot.nativex.substitution")

spring-core/src/main/java/org/springframework/util/CollectionUtils.java

@@ -62,6 +62,7 @@ public abstract class CollectionUtils {
 	 * @param collection the Collection to check
 	 * @return whether the given Collection is empty
 	 */
+	@Contract("null -> true")
 	public static boolean isEmpty(@Nullable Collection<?> collection) {
 		return (collection == null || collection.isEmpty());
 	}

spring-core/src/main/java/org/springframework/util/ObjectUtils.java

@@ -101,6 +101,7 @@ public static boolean isCompatibleWithThrowsClause(Throwable ex, @Nullable Class
 	 * either an Object array or a primitive array.
 	 * @param obj the object to check
 	 */
+	@Contract("null -> false")
 	public static boolean isArray(@Nullable Object obj) {
 		return (obj != null && obj.getClass().isArray());
 	}

spring-web/src/main/java/org/springframework/web/client/DefaultResponseErrorHandler.java

@@ -201,6 +201,7 @@ else if (statusCode.is5xxServerError()) {
 	 * {@link RestClientResponseException#setBodyConvertFunction(Function)}.
 	 * @since 6.0
 	 */
+	@SuppressWarnings("NullAway")
 	protected Function<ResolvableType, ?> initBodyConvertFunction(ClientHttpResponse response, byte[] body) {
 		Assert.state(!CollectionUtils.isEmpty(this.messageConverters), "Expected message converters");
 		return resolvableType -> {

spring-web/src/main/java/org/springframework/web/client/DefaultRestClient.java

@@ -522,6 +522,7 @@ else if (CollectionUtils.isEmpty(defaultHeaders)) {
 			}
 		}
 
+		@SuppressWarnings("NullAway")
 		private ClientHttpRequest createRequest(URI uri) throws IOException {
 			ClientHttpRequestFactory factory;
 			if (DefaultRestClient.this.interceptors != null) {

spring-web/src/main/java/org/springframework/web/context/request/RequestAttributesThreadLocalAccessor.java

@@ -18,6 +18,8 @@
 
 import io.micrometer.context.ThreadLocalAccessor;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Adapt {@link RequestContextHolder} to the {@link ThreadLocalAccessor} contract
  * to assist the Micrometer Context Propagation library with
@@ -40,6 +42,7 @@ public Object key() {
 	}
 
 	@Override
+	@Nullable
 	public RequestAttributes getValue() {
 		return RequestContextHolder.getRequestAttributes();
 	}

spring-web/src/main/java/org/springframework/web/context/request/async/StandardServletAsyncWebRequest.java

@@ -84,6 +84,7 @@ public StandardServletAsyncWebRequest(HttpServletRequest request, HttpServletRes
 	 * @param previousRequest the existing request from the last dispatch
 	 * @since 5.3.33
 	 */
+	@SuppressWarnings("NullAway")
 	StandardServletAsyncWebRequest(HttpServletRequest request, HttpServletResponse response,
 			@Nullable StandardServletAsyncWebRequest previousRequest) {
 
@@ -243,6 +244,7 @@ public void setAsyncWebRequest(StandardServletAsyncWebRequest asyncWebRequest) {
 		}
 
 		@Override
+		@SuppressWarnings("NullAway")
 		public ServletOutputStream getOutputStream() throws IOException {
 			int level = obtainLockAndCheckState();
 			try {
@@ -262,6 +264,7 @@ public ServletOutputStream getOutputStream() throws IOException {
 		}
 
 		@Override
+		@SuppressWarnings("NullAway")
 		public PrintWriter getWriter() throws IOException {
 			int level = obtainLockAndCheckState();
 			try {

spring-web/src/main/java/org/springframework/web/context/request/async/WebAsyncManager.java

@@ -287,6 +287,7 @@ public void startCallableProcessing(Callable<?> callable, Object... processingCo
 	 * via {@link #getConcurrentResultContext()}
 	 * @throws Exception if concurrent processing failed to start
 	 */
+	@SuppressWarnings("NullAway")
 	public void startCallableProcessing(final WebAsyncTask<?> webAsyncTask, Object... processingContext)
 			throws Exception {
 
@@ -408,6 +409,7 @@ private void setConcurrentResultAndDispatch(@Nullable Object result) {
 	 * @see #getConcurrentResult()
 	 * @see #getConcurrentResultContext()
 	 */
+	@SuppressWarnings("NullAway")
 	public void startDeferredResultProcessing(
 			final DeferredResult<?> deferredResult, Object... processingContext) throws Exception {
 

spring-web/src/main/java/org/springframework/web/context/support/ServletContextResourcePatternResolver.java

@@ -104,6 +104,7 @@ protected Set<Resource> doFindPathMatchingFileResources(Resource rootDirResource
 	 * @see ServletContextResource
 	 * @see jakarta.servlet.ServletContext#getResourcePaths
 	 */
+	@SuppressWarnings("NullAway")
 	protected void doRetrieveMatchingServletContextResources(
 			ServletContext servletContext, String fullPattern, String dir, Set<Resource> result)
 			throws IOException {

spring-web/src/main/java/org/springframework/web/cors/CorsConfiguration.java

@@ -171,6 +171,7 @@ public List<String> getAllowedOrigins() {
 	/**
 	 * Variant of {@link #setAllowedOrigins} for adding one origin at a time.
 	 */
+	@SuppressWarnings("NullAway")
 	public void addAllowedOrigin(@Nullable String origin) {
 		if (origin == null) {
 			return;
@@ -244,6 +245,7 @@ public List<String> getAllowedOriginPatterns() {
 	 * Variant of {@link #setAllowedOriginPatterns} for adding one origin at a time.
 	 * @since 5.3
 	 */
+	@SuppressWarnings("NullAway")
 	public void addAllowedOriginPattern(@Nullable String originPattern) {
 		if (originPattern == null) {
 			return;

spring-web/src/main/java/org/springframework/web/method/HandlerMethod.java

@@ -342,7 +342,7 @@ public String getShortLogMessage() {
 
 	@Override
 	public boolean equals(@Nullable Object other) {
-		return (this == other || (super.equals(other) && this.bean.equals(((HandlerMethod) other).bean)));
+		return (this == other || (super.equals(other) && other instanceof HandlerMethod otherMethod && this.bean.equals(otherMethod.bean)));
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/web/multipart/support/AbstractMultipartHttpServletRequest.java

@@ -136,6 +136,7 @@ protected final void setMultipartFiles(MultiValueMap<String, MultipartFile> mult
 	 * lazily initializing it if necessary.
 	 * @see #initializeMultipart()
 	 */
+	@SuppressWarnings("NullAway")
 	protected MultiValueMap<String, MultipartFile> getMultipartFiles() {
 		if (this.multipartFiles == null) {
 			initializeMultipart();

spring-web/src/main/java/org/springframework/web/multipart/support/StandardMultipartHttpServletRequest.java

@@ -137,6 +137,7 @@ protected void initializeMultipart() {
 	}
 
 	@Override
+	@SuppressWarnings("NullAway")
 	public Enumeration<String> getParameterNames() {
 		if (this.multipartParameterNames == null) {
 			initializeMultipart();
@@ -157,6 +158,7 @@ public Enumeration<String> getParameterNames() {
 	}
 
 	@Override
+	@SuppressWarnings("NullAway")
 	public Map<String, String[]> getParameterMap() {
 		if (this.multipartParameterNames == null) {
 			initializeMultipart();

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -152,6 +152,7 @@ public void setCodecConfigurer(ServerCodecConfigurer codecConfigurer) {
 	/**
 	 * Return the configured {@link ServerCodecConfigurer}.
 	 */
+	@SuppressWarnings("NullAway")
 	public ServerCodecConfigurer getCodecConfigurer() {
 		if (this.codecConfigurer == null) {
 			setCodecConfigurer(ServerCodecConfigurer.create());

spring-web/src/main/java/org/springframework/web/server/session/InMemoryWebSessionStore.java

@@ -189,6 +189,7 @@ public InMemoryWebSession(Instant creationTime) {
 		}
 
 		@Override
+		@SuppressWarnings("NullAway")
 		public String getId() {
 			return this.id.get();
 		}
@@ -224,6 +225,7 @@ public void start() {
 		}
 
 		@Override
+		@SuppressWarnings("NullAway")
 		public boolean isStarted() {
 			return this.state.get().equals(State.STARTED) || !getAttributes().isEmpty();
 		}
@@ -252,6 +254,7 @@ public Mono<Void> invalidate() {
 		}
 
 		@Override
+		@SuppressWarnings("NullAway")
 		public Mono<Void> save() {
 
 			checkMaxSessionsLimit();
@@ -289,6 +292,7 @@ public boolean isExpired() {
 			return isExpired(clock.instant());
 		}
 
+		@SuppressWarnings("NullAway")
 		private boolean isExpired(Instant now) {
 			if (this.state.get().equals(State.EXPIRED)) {
 				return true;

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceMethod.java

@@ -223,6 +223,7 @@ private static HttpMethod initHttpMethod(@Nullable HttpExchange typeAnnotation,
 		}
 
 		@Nullable
+		@SuppressWarnings("NullAway")
 		private static String initUrl(
 				@Nullable HttpExchange typeAnnotation, HttpExchange methodAnnotation,
 				@Nullable StringValueResolver embeddedValueResolver) {

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceProxyFactory.java

@@ -251,7 +251,7 @@ public HttpServiceProxyFactory build() {
 					this.exchangeAdapter, initArgumentResolvers(), this.embeddedValueResolver);
 		}
 
-		@SuppressWarnings("DataFlowIssue")
+		@SuppressWarnings({"DataFlowIssue", "NullAway"})
 		private List<HttpServiceArgumentResolver> initArgumentResolvers() {
 
 			// Custom