/**
  * @param AbstractCrudObject $object
  * @param array $diff
  * @return array
  */
 private function extractDiffFromObject(AbstractCrudObject $object, array $diff)
 {
     $sub_diff = array();
     foreach ($object->getData() as $key => $val) {
         if (array_key_exists($key, $diff)) {
             $sub_diff[$key] = $val;
         }
     }
     return $sub_diff + array_combine(array_keys($diff), array_fill(0, count($diff), null));
 }