Avoid return value reference in potentially cached MethodParameter in…

…stance

Closes spring-projectsgh-28232

(cherry picked from commit eefdd2c)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -270,16 +270,16 @@ public <T extends Annotation> T getMethodAnnotation(Class<T> annotationType) {
 	 */
 	private class ReturnValueMethodParameter extends HandlerMethodParameter {
 
-		private final Object returnValue;
+		private final Class<?> returnValueType;
 
 		public ReturnValueMethodParameter(Object returnValue) {
 			super(-1);
-			this.returnValue = returnValue;
+			this.returnValueType = (returnValue != null ? returnValue.getClass() : null);
 		}
 
 		@Override
 		public Class<?> getParameterType() {
-			return (this.returnValue != null ? this.returnValue.getClass() : super.getParameterType());
+			return (this.returnValueType != null ? this.returnValueType : super.getParameterType());
 		}
 	}