/**
  * Check if there are changes between old and new value for this field
  *
  * @param Tracker_Artifact_ChangesetValue $old_value The data stored in the db
  * @param mixed                           $new_value May be string or array
  *
  * @return bool true if there are differences
  */
 public function hasChanges(Tracker_Artifact_ChangesetValue $old_value, $new_value)
 {
     return $old_value->getNumeric() != $new_value;
 }