protected function prepareCollection()
    {
        $need_conversion = false;
        $first_row = $this->data->first();

        if (!$first_row) {
            return;
        }

        foreach ($first_row as $item) {
            if (!is_string($item)) {
                $need_conversion = true;
            }
        }
        if ($need_conversion) {
            $this->transform();
        }
    }