src/java.base/share/classes/java/util/Comparators.java

*** 60,69 ****
--- 60,70 ----
  
      /**
       * 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
          private final Comparator<T> real;