@GwtIncompatible
    @J2ktIncompatible
        private void writeObject(ObjectOutputStream stream) throws IOException {
      stream.defaultWriteObject();
      stream.writeObject(factory);
      stream.writeObject(backingMap());
    }

    @GwtIncompatible
    @J2ktIncompatible
        @SuppressWarnings("unchecked") // reading data stored by writeObject

    @GwtIncompatible
    @J2ktIncompatible
        private void writeObject(ObjectOutputStream stream) throws IOException {
      stream.defaultWriteObject();
      stream.writeObject(factory);
      stream.writeObject(backingMap());
    }

    @GwtIncompatible
    @J2ktIncompatible
        @SuppressWarnings("unchecked") // reading data stored by writeObject

    void writeMapTo(ObjectOutputStream out) throws IOException {
      out.writeInt(delegate.size());
      for (Entry<K, V> entry : delegate.entrySet()) {
        out.writeObject(entry.getKey());
        out.writeObject(entry.getValue());
      }
      out.writeObject(null); // terminate entries
    }

    @J2ktIncompatible // java.io.ObjectInputStream
    MapMaker readMapMaker(ObjectInputStream in) throws IOException {