private function normalizeScheme($scheme)
    {
        if (!is_string($scheme) && !method_exists($scheme, '__toString')) {
            throw new InvalidArgumentException('Uri scheme must be a string');
        }

        $scheme = str_replace('://', '', strtolower((string) $scheme));
        if (!isset($this->validSchema[$scheme])) {
            throw new InvalidArgumentException('Uri scheme must be one of: "", "https", "http"');
        }

        return $scheme;
    }