/**
  * get the filter group object
  *
  * @param $filterModel
  * @return Tinebase_Model_Filter_FilterGroup
  */
 protected function _getFilterObject($filterModel)
 {
     if (!class_exists($filterModel)) {
         $configuredModel = preg_replace('/Filter$/', '', $filterModel);
         // TODO check if model class exists?
         //if (class_exists($configuredModel))
         // use generic filter model
         $filter = new Tinebase_Model_Filter_FilterGroup();
         $filter->setConfiguredModel($configuredModel);
     } else {
         $filter = new $filterModel();
     }
     return $filter;
 }