protected function getCopy(ObjectId $origOID) {
    $copyOID = $this->getCopyOID($origOID);
    if ($copyOID != null) {
      $persistenceFacade = $this->getPersistenceFacade();
      $nodeCopy = $persistenceFacade->load($copyOID);
      return $nodeCopy;
    }
    else {
      return null;
    }
  }