public function getOutputFilename()
    {
        $result = $this->outputFilename;
        if ($result === '') {
            $config = $this->app->make('config');
            $relativeName = '/' . ltrim(str_replace(DIRECTORY_SEPARATOR, '/', (string) $config->get('concrete.sitemap_xml.file')), '/');
            if ($relativeName === '/') {
                $relativeName = '/sitemap.xml';
            }
            $result = rtrim(DIR_BASE, '/') . $relativeName;
        }

        return $result;
    }