private function get_query_args()
 {
     $defaults = MS_Model_Invoice::get_query_args();
     lib3()->array->equip_request('s');
     $per_page = $this->get_items_per_page('invoice_per_page', self::DEFAULT_PAGE_SIZE);
     $current_page = $this->get_pagenum();
     $args = array('posts_per_page' => $per_page, 'offset' => ($current_page - 1) * $per_page);
     // Filter by search-term
     $search_filter = $_REQUEST['s'];
     if (!empty($search_filter)) {
         $this->search_string = $search_filter;
     }
     $args = wp_parse_args($args, $defaults);
     return $args;
 }