public function getLastOpenItem(Tinebase_Record_RecordSet $batchJobMonitionItems)
 {
     if ($batchJobMonitionItems->getCount() == 0) {
         throw new Billing_Exception_OpenItem('Recordset does not contain any monition open items and therefore no related order.');
     }
     $batchJobMonitionItems->sort('open_item_id', 'DESC');
     $record = $batchJobMonitionItems->getFirstRecord();
     $openItem = $record->getForeignRecord('open_item_id', Billing_Controller_OpenItem::getInstance());
     return $openItem;
 }