code: protected function normalizeFilter()
      {
          $this->substituteField($this->filter, 'GROUPS', 'GROUPS_ID');
          $this->substituteField($this->filter, 'GROUP_ID', 'GROUPS_ID');
  
          return $this->filter;
      }
docs: Normalize filter before sending it to getList.
  This prevents some inconsistency.
  
  @return array