@Override
  @J2ktIncompatible // serialization
  @GwtIncompatible // serialization
  Object writeReplace() {
    return super.writeReplace();
  }

  // No longer used for new writes, but kept so that old data can still be read.
  @GwtIncompatible // serialization
  @J2ktIncompatible
  @SuppressWarnings("unused")
  private static class SerializedForm<V> implements Serializable {