public static function getSspPath($sspPath)
    {

        if ($sspPath === Null) {
            $sspPath = getenv(self::SSP_PATH_ENV);
        }

        if (!$sspPath) {
            throw new InvalidSspPathException(
                'Invalid path for simplesamlphp.' . PHP_EOL .
                'Cannot be null or evaluate to false.',
                1476967000
            );
        }

        return $sspPath;
    }