/**
  * getSaveData()
  * overwrite FrontendModule::getSaveData
  */
 public function getSaveData($mData)
 {
     $oFlash = new Flash($mData);
     $oFlash->checkForValue(self::DISPLAY_MODE, 'display_mode_required');
     if ($mData['display_mode'] !== 'newsletter_unsubscribe') {
         $oFlash->checkForValue('subscriber_group_id', 'subscriber_group_required');
     }
     $oFlash->finishReporting();
     if ($oFlash->hasMessages()) {
         throw new ValidationException($oFlash);
     }
     return parent::getSaveData($mData);
 }