public function handle($model)
    {
        if (! $model -> isUserstamping()) {
            return;
        }

        if (is_null($model -> {$model -> getCreatedByColumn()})) {
            $model -> {$model -> getCreatedByColumn()} = auth() -> id();
        }

        if (is_null($model -> {$model -> getUpdatedByColumn()}) && ! is_null($model -> getUpdatedByColumn())) {
            $model -> {$model -> getUpdatedByColumn()} = auth() -> id();
        }
    }