Annotate Object#equals parameter with @Nullable

Closes gh-23093

spring-messaging/src/main/java/org/springframework/messaging/MessageHeaders.java

@@ -320,7 +320,7 @@ public class MessageHeaders implements Map<String, Object>, Serializable {
 	// equals, hashCode, toString
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		return (this == other ||
 				(other instanceof MessageHeaders && this.headers.equals(((MessageHeaders) other).headers)));
 	}

spring-messaging/src/main/java/org/springframework/messaging/handler/CompositeMessageCondition.java

@@ -21,6 +21,7 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Collectors;
 
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 
@@ -126,7 +127,7 @@ public class CompositeMessageCondition implements MessageCondition<CompositeMess
 
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}

spring-messaging/src/main/java/org/springframework/messaging/handler/HandlerMethod.java

@@ -303,7 +303,7 @@ public class HandlerMethod {
 
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}

spring-messaging/src/main/java/org/springframework/messaging/simp/SimpMessageMappingInfo.java

@@ -77,7 +77,7 @@ public class SimpMessageMappingInfo implements MessageCondition<SimpMessageMappi
 
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/DefaultSubscriptionRegistry.java

@@ -512,7 +512,7 @@ public class DefaultSubscriptionRegistry extends AbstractSubscriptionRegistry {
 		}
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			return (this == other || (other instanceof Subscription && this.id.equals(((Subscription) other).id)));
 		}
 

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

@@ -552,7 +552,7 @@ public class StompHeaders implements MultiValueMap<String, String>, Serializable
 
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		return (this == other || (other instanceof StompHeaders &&
 				this.headers.equals(((StompHeaders) other).headers)));
 	}

spring-messaging/src/main/java/org/springframework/messaging/simp/user/MultiServerUserRegistry.java

@@ -357,7 +357,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			return (this == other || (other instanceof SimpUser && this.name.equals(((SimpUser) other).getName())));
 		}
 
@@ -441,7 +441,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 		}
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			return (this == other || (other instanceof SimpSession && getId().equals(((SimpSession) other).getId())));
 		}
 
@@ -515,7 +515,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 		}
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			if (this == other) {
 				return true;
 			}

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

@@ -19,6 +19,7 @@ package org.springframework.messaging.support;
 import java.io.Serializable;
 import java.util.Map;
 
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHeaders;
 import org.springframework.util.Assert;
@@ -85,7 +86,7 @@ public class GenericMessage<T> implements Message<T>, Serializable {
 	}
 
 
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}