$controller = unserialize(base64_decode($controllerrec->controller));

        if (!is_object($controller)) {

            // The controller field of the table did not contain a serialized object.

            // It is made empty after it has been used successfully, it is likely that

            // the user has pressed the browser back button at some point.

            throw new backup_dbops_exception('backup_controller_dbops_loading_invalid_controller');

        }