function update_unset_billing_values()
 {
     ajx_current("empty");
     if (!logged_user()->isAdministrator()) {
         flash_error(lang("no access permissions"));
         return;
     }
     try {
         DB::beginWork();
         $count = Timeslots::updateBillingValues();
         DB::commit();
         flash_success(lang("success update billing values", $count));
     } catch (Exception $e) {
         DB::rollback();
         flash_error($e->getMessage());
     }
 }