Inheritance: extends Massive\Bundle\SearchBundle\Search\Document
 /**
  * Map the creator and changer to the document.
  *
  * @param Document      $document
  * @param UserInterface $creator
  * @param UserInterface $changer
  */
 private function mapCreatorAndChanger(Document $document, UserInterface $creator = null, UserInterface $changer = null)
 {
     $document->addField($this->factory->createField('changer', $changer ? $changer->getUsername() : null, 'string'));
     $document->addField($this->factory->createField('changer_id', $changer ? $changer->getId() : null, 'string'));
     $document->addField($this->factory->createField('creator', $creator ? $creator->getUsername() : null, 'string'));
     $document->addField($this->factory->createField('creator_id', $creator ? $creator->getId() : null, 'string'));
 }