Object writeReplace() {
    return new EntrySetSerializedForm<>(map());
  }

  @GwtIncompatible
  @J2ktIncompatible
    private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Use EntrySetSerializedForm");
  }

  @GwtIncompatible
  @J2ktIncompatible
  private static final class EntrySetSerializedForm<K, V> implements Serializable {