private function getAugmentedFieldValue($artifact_id, Tracker_Report $report)
 {
     $result = '';
     EventManager::instance()->processEvent(TRACKER_EVENT_FIELD_AUGMENT_DATA_FOR_REPORT, array('additional_criteria' => $report->getAdditionalCriteria(), 'result' => &$result, 'artifact_id' => $artifact_id, 'field' => $this));
     return $result;
 }