public static function get_converter($name, $tempdir, $logger = null) {
        global $CFG;

        $name = clean_param($name, PARAM_SAFEDIR);

        $classfile = "$CFG->dirroot/backup/converter/$name/lib.php";
        $classname = "{$name}_converter";

        if (!file_exists($classfile)) {
            throw new coding_exception("Converter factory error: class file not found $classfile");
        }
        require_once($classfile);

        if (!class_exists($classname)) {
            throw new coding_exception("Converter factory error: class not found $classname");
        }

        return new $classname($tempdir, $logger);
    }