public function unconfirmedTransactions($address, $hash = null)
    {
        $params = ["address" => $address];

        if ($hash !== null)
            $params["hash"] = $hash;

        $apiUrl = $this->getPath('unconfirmedTransactions', $params);
        $response = $this->api->getJSON($apiUrl);

        //XXX include Error checks
        $data = json_decode($response, true);
        return $this->createTransactionCollection($object['data']); //XXX brr => error/content validation first
    }