/**
  * merge record / skip if no diff
  * 
  * @param Tinebase_Record_Abstract $updateRecord
  * @param Tinebase_Record_Abstract $mergeRecord
  * @return Tinebase_Record_Abstract
  */
 protected function _mergeRecord($updateRecord, $mergeRecord)
 {
     $omitFields = array('creation_time', 'created_by', 'last_modified_time', 'last_modified_by', 'seq', 'id');
     $diff = $updateRecord->diff($mergeRecord, $omitFields);
     if (!$diff || $diff->isEmpty()) {
         if (Tinebase_Core::isLogLevel(Zend_Log::DEBUG)) {
             Tinebase_Core::getLogger()->debug(__METHOD__ . '::' . __LINE__ . ' Records are identical, no need to update');
         }
         return null;
     } else {
         if (Tinebase_Core::isLogLevel(Zend_Log::TRACE)) {
             Tinebase_Core::getLogger()->trace(__METHOD__ . '::' . __LINE__ . ' Got diff: ' . print_r($diff->diff, TRUE));
         }
     }
     return $updateRecord->merge($mergeRecord, $diff);
 }