public static function prepare_filter_values_for_form(tour $tour, \stdClass $data) {
        $filtername = static::get_filter_name();
        $key = "filter_{$filtername}";
        $values = $tour->get_filter_values($filtername);
        if (empty($values)) {
            $values = 0;
        }
        $data->$key = $values;
        return $data;
    }