--- old/src/java.base/share/classes/java/util/Comparators.java	2019-08-27 17:28:51.270324386 -0700
+++ new/src/java.base/share/classes/java/util/Comparators.java	2019-08-27 17:28:51.066324386 -0700
@@ -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