Perform NullAway build-time checks in spring-webflux

See gh-32475

gradle/spring-module.gradle

@@ -117,7 +117,8 @@ tasks.withType(JavaCompile).configureEach {
     options.errorprone {
     	disableAllChecks = true
         option("NullAway:CustomContractAnnotations", "org.springframework.lang.Contract")
-        option("NullAway:AnnotatedPackages", "org.springframework.core,org.springframework.expression")
+        option("NullAway:AnnotatedPackages", "org.springframework.core,org.springframework.expression," +
+        		"org.springframework.web.reactive")
         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-webflux/src/main/java/org/springframework/web/reactive/DispatcherHandler.java

@@ -171,9 +171,10 @@ public class DispatcherHandler implements WebHandler, PreFlightRequestHandler, A
 		}
 		return resultMono.flatMap(result -> {
 			Mono<Void> voidMono = handleResult(exchange, result, "Handler " + result.getHandler());
-			if (result.getExceptionHandler() != null) {
+			DispatchExceptionHandler exceptionHandler = result.getExceptionHandler();
+			if (exceptionHandler != null) {
 				voidMono = voidMono.onErrorResume(ex ->
-						result.getExceptionHandler().handleError(exchange, ex).flatMap(result2 ->
+						exceptionHandler.handleError(exchange, ex).flatMap(result2 ->
 								handleResult(exchange, result2, "Exception handler " +
 										result2.getHandler() + ", error=\"" + ex.getMessage() + "\"")));
 			}

spring-webflux/src/main/java/org/springframework/web/reactive/config/ResourceChainRegistration.java

@@ -64,6 +64,7 @@ public class ResourceChainRegistration {
 		this(cacheResources, cacheResources ? new ConcurrentMapCache(DEFAULT_CACHE_NAME) : null);
 	}
 
+	@SuppressWarnings("NullAway")
 	public ResourceChainRegistration(boolean cacheResources, @Nullable Cache cache) {
 		Assert.isTrue(!cacheResources || cache != null, "'cache' is required when cacheResources=true");
 		if (cacheResources) {

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientResponseBuilder.java

@@ -137,7 +137,7 @@ final class DefaultClientResponseBuilder implements ClientResponse.Builder {
 		return this;
 	}
 
-	@SuppressWarnings("ConstantConditions")
+	@SuppressWarnings({"ConstantConditions", "NullAway"})
 	private HttpHeaders getHeaders() {
 		if (this.headers == null) {
 			this.headers = new HttpHeaders(this.originalResponse.headers().asHttpHeaders());
@@ -159,7 +159,7 @@ final class DefaultClientResponseBuilder implements ClientResponse.Builder {
 		return this;
 	}
 
-	@SuppressWarnings("ConstantConditions")
+	@SuppressWarnings({"ConstantConditions", "NullAway"})
 	private MultiValueMap<String, ResponseCookie> getCookies() {
 		if (this.cookies == null) {
 			this.cookies = new LinkedMultiValueMap<>(this.originalResponse.cookies());
@@ -256,13 +256,13 @@ final class DefaultClientResponseBuilder implements ClientResponse.Builder {
 		}
 
 		@Override
-		@SuppressWarnings("ConstantConditions")
+		@SuppressWarnings({"ConstantConditions", "NullAway"})
 		public HttpHeaders getHeaders() {
 			return (this.headers != null ? this.headers : this.originalResponse.headers().asHttpHeaders());
 		}
 
 		@Override
-		@SuppressWarnings("ConstantConditions")
+		@SuppressWarnings({"ConstantConditions", "NullAway"})
 		public MultiValueMap<String, ResponseCookie> getCookies() {
 			return (this.cookies != null ? this.cookies : this.originalResponse.cookies());
 		}

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceWebHandler.java

@@ -334,6 +334,7 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 	 * @param mediaTypes media type mappings
 	 * @since 5.3.2
 	 */
+	@SuppressWarnings("NullAway")
 	public void setMediaTypes(Map<String, MediaType> mediaTypes) {
 		if (this.mediaTypes == null) {
 			this.mediaTypes = new HashMap<>(mediaTypes.size());
@@ -483,6 +484,7 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 				});
 	}
 
+	@SuppressWarnings("NullAway")
 	protected Mono<Resource> getResource(ServerWebExchange exchange) {
 		String rawPath = getResourcePath(exchange);
 		String path = processPath(rawPath);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/AbstractHandlerMethodMapping.java

@@ -361,6 +361,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 		}
 	}
 
+	@SuppressWarnings("NullAway")
 	private void addMatchingMappings(Collection<T> mappings, List<Match> matches, ServerWebExchange exchange) {
 		for (T mapping : mappings) {
 			T match = getMatchingMapping(mapping, exchange);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -46,6 +46,7 @@ import org.springframework.core.ReactiveAdapter;
 import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.http.HttpStatusCode;
 import org.springframework.http.server.reactive.ServerHttpResponse;
+import org.springframework.lang.Contract;
 import org.springframework.lang.Nullable;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
@@ -161,7 +162,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 	 * @param providedArgs optional list of argument values to match by type
 	 * @return a Mono with a {@link HandlerResult}
 	 */
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({"unchecked", "NullAway"})
 	public Mono<HandlerResult> invoke(
 			ServerWebExchange exchange, BindingContext bindingContext, Object... providedArgs) {
 
@@ -261,6 +262,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		}
 	}
 
+	@Contract("_, null -> false")
 	private static boolean isAsyncVoidReturnType(MethodParameter returnType, @Nullable ReactiveAdapter adapter) {
 		if (adapter != null && adapter.supportsEmpty()) {
 			if (adapter.isNoValue()) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/AbstractMessageWriterResultHandler.java

@@ -165,7 +165,7 @@ public abstract class AbstractMessageWriterResultHandler extends HandlerResultHa
 	 * @return indicates completion or error
 	 * @since 5.0.2
 	 */
-	@SuppressWarnings({"rawtypes", "unchecked", "ConstantConditions"})
+	@SuppressWarnings({"rawtypes", "unchecked", "ConstantConditions", "NullAway"})
 	protected Mono<Void> writeBody(@Nullable Object body, MethodParameter bodyParameter,
 			@Nullable MethodParameter actualParam, ServerWebExchange exchange) {
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ControllerMethodResolver.java

@@ -375,6 +375,7 @@ class ControllerMethodResolver {
 	 * if {@code null}, check only {@code @ControllerAdvice} classes.
 	 */
 	@Nullable
+	@SuppressWarnings("NullAway")
 	public InvocableHandlerMethod getExceptionHandlerMethod(Throwable ex, @Nullable HandlerMethod handlerMethod) {
 
 		Class<?> handlerType = (handlerMethod != null ? handlerMethod.getBeanType() : null);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ResponseEntityResultHandler.java

@@ -128,7 +128,7 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 
 
 	@Override
-	@SuppressWarnings("ConstantConditions")
+	@SuppressWarnings({"ConstantConditions", "NullAway"})
 	public Mono<Void> handleResult(ServerWebExchange exchange, HandlerResult result) {
 
 		Mono<?> returnValueMono;

spring-webflux/src/main/java/org/springframework/web/reactive/socket/adapter/Netty5WebSocketSessionSupport.java

@@ -28,6 +28,7 @@ import io.netty5.handler.codec.http.websocketx.WebSocketFrame;
 
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.Netty5DataBufferFactory;
+import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.reactive.socket.HandshakeInfo;
 import org.springframework.web.reactive.socket.WebSocketMessage;
@@ -76,7 +77,9 @@ public abstract class Netty5WebSocketSessionSupport<T> extends AbstractWebSocket
 
 	protected WebSocketMessage toMessage(WebSocketFrame frame) {
 		DataBuffer payload = bufferFactory().wrap(frame.binaryData());
-		return new WebSocketMessage(messageTypes.get(frame.getClass()), payload, frame);
+		WebSocketMessage.Type messageType = messageTypes.get(frame.getClass());
+		Assert.state(messageType != null, "Unexpected message type");
+		return new WebSocketMessage(messageType, payload, frame);
 	}
 
 	protected WebSocketFrame toFrame(WebSocketMessage message) {

spring-webflux/src/main/java/org/springframework/web/reactive/socket/adapter/NettyWebSocketSessionSupport.java

@@ -28,6 +28,7 @@ import io.netty.handler.codec.http.websocketx.WebSocketFrame;
 
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.NettyDataBufferFactory;
+import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.reactive.socket.HandshakeInfo;
 import org.springframework.web.reactive.socket.WebSocketMessage;
@@ -74,7 +75,9 @@ public abstract class NettyWebSocketSessionSupport<T> extends AbstractWebSocketS
 
 	protected WebSocketMessage toMessage(WebSocketFrame frame) {
 		DataBuffer payload = bufferFactory().wrap(frame.content());
-		return new WebSocketMessage(messageTypes.get(frame.getClass()), payload, frame);
+		WebSocketMessage.Type messageType = messageTypes.get(frame.getClass());
+		Assert.state(messageType != null, "Unexpected message type");
+		return new WebSocketMessage(messageType, payload, frame);
 	}
 
 	protected WebSocketFrame toFrame(WebSocketMessage message) {

spring-webflux/src/main/java/org/springframework/web/reactive/socket/adapter/StandardWebSocketHandlerAdapter.java

@@ -65,6 +65,7 @@ public class StandardWebSocketHandlerAdapter extends Endpoint {
 
 
 	@Override
+	@SuppressWarnings("NullAway")
 	public void onOpen(Session session, EndpointConfig config) {
 		this.delegateSession = this.sessionFactory.apply(session);
 		Assert.state(this.delegateSession != null, "No delegate session");

spring-webflux/src/main/java/org/springframework/web/reactive/socket/server/support/HandshakeWebSocketService.java

@@ -244,6 +244,7 @@ public class HandshakeWebSocketService implements WebSocketService, Lifecycle {
 		return null;
 	}
 
+	@SuppressWarnings("NullAway")
 	private Mono<Map<String, Object>> initAttributes(ServerWebExchange exchange) {
 		if (this.sessionAttributePredicate == null) {
 			return EMPTY_ATTRIBUTES;