public function getClass(string $oid)
    {
        // if OID is provided by this factory
        if (array_key_exists($oid, self::MAP_OID_TO_CLASS)) {
            return self::MAP_OID_TO_CLASS[$oid];
        }
        // try additional providers
        foreach ($this->_additionalProviders as $provider) {
            if ($provider->supportsOID($oid)) {
                return $provider->getClassByOID($oid);
            }
        }
        return null;
    }