Add javadoc for body parameter

See gh-26613

spring-web/src/main/java/org/springframework/http/ResponseEntity.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -237,8 +237,9 @@ public static BodyBuilder ok() {
 	}
 
 	/**
-	 * A shortcut for creating a {@code ResponseEntity} with the given body and
-	 * the status set to {@linkplain HttpStatus#OK OK}.
+	 * A shortcut for creating a {@code ResponseEntity} with the given body
+	 * and the status set to {@linkplain HttpStatus#OK OK}.
+	 * @param body the body of the response entity (possibly empty)
 	 * @return the created {@code ResponseEntity}
 	 * @since 4.1
 	 */