code: @Override
    public void writeExternal(ObjectOutput out) throws IOException {
      super.writeExternal(out);
      splitHistory.writeExternal(out);
    }
docs: Calls the super method and writes the MBR object of this entry to the
  specified output stream.
  
  @param out the stream to write the object to
  @throws java.io.IOException Includes any I/O exceptions that may occur