/**
  * this method is called before save the duplicate document.
  * If this method not override in the document service, the document isn't duplicable.
  * An IllegalOperationException is so launched.
  *
  * @param form_persistentdocument_baseform $newDocument
  * @param form_persistentdocument_baseform $originalDocument
  * @param Integer $parentNodeId
  *
  * @throws IllegalOperationException
  */
 protected function preDuplicate($newDocument, $originalDocument, $parentNodeId)
 {
     $newDocument->setFormid(null);
     $newDocument->setAcknowledgmentNotification(null);
 }