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

    @GwtIncompatible // java.io.ObjectInputStream
    @J2ktIncompatible
    @SuppressWarnings("unchecked") // reading data stored by writeObject

    }

    // Serialization invokes writeObject only when it's private.
    // The SynchronizedObject subclasses don't need a writeObject method since
    // they don't contain any non-transient member variables, while the
    // following writeObject() handles the SynchronizedObject members.

    @GwtIncompatible // java.io.ObjectOutputStream
    @J2ktIncompatible
    private void writeObject(ObjectOutputStream stream) throws IOException {

    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
    }

    @SuppressWarnings("deprecation") // serialization of deprecated feature
    @J2ktIncompatible // java.io.ObjectInputStream

      throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ObjectOutputStream out = new ObjectOutputStream(bos);

    out.writeObject(original);

    byte[] handle = toByteArray(baseWireHandle + handleOffset);
    byte[] ref = prepended(TC_REFERENCE, handle);
    bos.write(ref);

    return bos.toByteArray();
  }