Filter out null WebSocketSession attributes

Closes gh-29315

spring-websocket/src/main/java/org/springframework/web/socket/adapter/AbstractWebSocketSession.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -62,7 +62,9 @@ public abstract class AbstractWebSocketSession<T> implements NativeWebSocketSess
 	 */
 	public AbstractWebSocketSession(@Nullable Map<String, Object> attributes) {
 		if (attributes != null) {
-			this.attributes.putAll(attributes);
+			attributes.entrySet().stream()
+					.filter(entry -> (entry.getKey() != null && entry.getValue() != null))
+					.forEach(entry -> this.attributes.put(entry.getKey(), entry.getValue()));
 		}
 	}