private function getTemporaryFolder()
    {
        $tempFolder = sys_get_temp_dir() . '/phpspreadsheet';
        if (!is_dir($tempFolder)) {
            if (!mkdir($tempFolder) && !is_dir($tempFolder)) {
                throw new \RuntimeException(sprintf('Directory "%s" was not created', $tempFolder));
            }
        }

        return $tempFolder;
    }