@SuppressWarnings("unchecked") // reading data stored by writeMultimap
      K key = (K) stream.readObject();
      Collection<V> values = multimap.get(key);
      int valueCount = stream.readInt();
      for (int j = 0; j < valueCount; j++) {
        @SuppressWarnings("unchecked") // reading data stored by writeMultimap
        V value = (V) stream.readObject();
        values.add(value);
      }
    }

   */
  @GwtIncompatible
  @J2ktIncompatible
    private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    Serialization.writeMultimap(this, stream);
  }

  @GwtIncompatible
  @J2ktIncompatible
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
    stream.defaultReadObject();