src/java.base/share/classes/java/io/ObjectOutputStream.java

@@ -877,10 +877,14 @@
      * to ObjectOutput.
      *
      * @since 1.2
      */
     public abstract static class PutField {
+        /**
+         * Constructor for subclasses to call.
+         */
+        public PutField() {}
 
         /**
          * Put the value of the named boolean field into the persistent field.
          *
          * @param  name the name of the serializable field