protected static function _generateReturnType($method)
    {
        if (Suite::$PHP < 7) {
            return '';
        }
        $type = $method->getReturnType();
        $allowsNull = '';
        if ($type) {
            if (method_exists($type, 'allowsNull') && $type->allowsNull()) {
                $allowsNull = '?';
            }
            if (!$type->isBuiltin()) {
                $type = '\\' . $type;
            }
            if (defined('HHVM_VERSION')) {
                $type = preg_replace('~\\\?HH\\\(mixed|void)?~', '', $type);
            }
        }
        return $type ? ": {$allowsNull}{$type} " : '';
    }