Perform NullAway build-time checks in spring-messaging

See gh-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,org.springframework.jms")
+        		"org.springframework.web,org.springframework.jms,org.springframework.messaging")
         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-messaging/src/main/java/org/springframework/messaging/handler/HandlerMethod.java

@@ -196,7 +196,8 @@ public class HandlerMethod extends AnnotatedMethod {
 
 	@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-messaging/src/main/java/org/springframework/messaging/handler/annotation/reactive/MessageMappingMessageHandler.java

@@ -305,6 +305,7 @@ public class MessageMappingMessageHandler extends AbstractMethodMessageHandler<C
 	 * @param destinations the destinations
 	 * @return new array with the processed destinations or the same array
 	 */
+	@SuppressWarnings("NullAway")
 	protected String[] processDestinations(String[] destinations) {
 		if (this.valueResolver != null) {
 			destinations = Arrays.stream(destinations)

spring-messaging/src/main/java/org/springframework/messaging/handler/invocation/AbstractMethodMessageHandler.java

@@ -522,6 +522,7 @@ public abstract class AbstractMethodMessageHandler<T>
 		handleMatch(bestMatch.mapping, bestMatch.handlerMethod, lookupDestination, message);
 	}
 
+	@SuppressWarnings("NullAway")
 	private void addMatchesToCollection(Collection<T> mappingsToCheck, Message<?> message, List<Match> matches) {
 		for (T mapping : mappingsToCheck) {
 			T match = getMatchingMapping(mapping, message);

spring-messaging/src/main/java/org/springframework/messaging/handler/invocation/reactive/AbstractMethodMessageHandler.java

@@ -505,6 +505,7 @@ public abstract class AbstractMethodMessageHandler<T>
 	@Nullable
 	protected abstract RouteMatcher.Route getDestination(Message<?> message);
 
+	@SuppressWarnings("NullAway")
 	private void addMatchesToCollection(
 			Collection<T> mappingsToCheck, Message<?> message, List<Match<T>> matches) {
 

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompDecoder.java

@@ -130,6 +130,7 @@ public class StompDecoder {
 	 * Decode a single STOMP frame from the given {@code byteBuffer} into a {@link Message}.
 	 */
 	@Nullable
+	@SuppressWarnings("NullAway")
 	private Message<byte[]> decodeMessage(ByteBuffer byteBuffer, @Nullable MultiValueMap<String, String> headers) {
 		Message<byte[]> decodedMessage = null;
 		skipEol(byteBuffer);

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompHeaderAccessor.java

@@ -237,6 +237,7 @@ public class StompHeaderAccessor extends SimpMessageHeaderAccessor {
 		return (SimpMessageType.HEARTBEAT == getMessageType());
 	}
 
+	@SuppressWarnings("NullAway")
 	public long[] getHeartbeat() {
 		String rawValue = getFirstNativeHeader(STOMP_HEARTBEAT_HEADER);
 		int pos = (rawValue != null ? rawValue.indexOf(',') : -1);

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompHeaders.java

@@ -278,6 +278,7 @@ public class StompHeaders implements MultiValueMap<String, String>, Serializable
 	 * Get the heartbeat header.
 	 */
 	@Nullable
+	@SuppressWarnings("NullAway")
 	public long[] getHeartbeat() {
 		String rawValue = getFirst(HEARTBEAT);
 		int pos = (rawValue != null ? rawValue.indexOf(',') : -1);
@@ -514,6 +515,7 @@ public class StompHeaders implements MultiValueMap<String, String>, Serializable
 	}
 
 	@Override
+	@Nullable
 	public List<String> get(Object key) {
 		return this.headers.get(key);
 	}

spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java

@@ -645,6 +645,7 @@ public class MessageHeaderAccessor {
 			return super.getRawHeaders();
 		}
 
+		@SuppressWarnings("NullAway")
 		public void setImmutable() {
 			if (!this.mutable) {
 				return;