--- a/src/java.base/share/classes/java/util/Comparators.java	Thu Aug 29 18:52:30 2019 -0400
+++ b/src/java.base/share/classes/java/util/Comparators.java	Thu Aug 29 16:31:34 2019 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -62,6 +62,7 @@
      * Null-friendly comparators
      */
     static final class NullComparator<T> implements Comparator<T>, Serializable {
+        @java.io.Serial
         private static final long serialVersionUID = -7569533591570686392L;
         private final boolean nullFirst;
         // if null, non-null Ts are considered equal