Category validation

/*make categories required for event submission*/
function my_em_validate($result,$EM_Event){
  if( empty($EM_Event->get_categories()->categories) ){
     $EM_Event->add_error( __("category is required.", "dbem") );
     return false;
  }
  return $result;
}
add_filter('em_event_validate_meta','my_em_validate',10,2);