@Override
  @J2ktIncompatible // serialization
  Object writeReplace() {
    return new EnumSerializedForm<>(delegate);
  }

  @J2ktIncompatible // serialization
  private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Use EnumSerializedForm");
  }

  /*
   * This class is used to serialize ImmutableEnumMap instances.
   */