执行下面语句时，返回 []，请问怎么解决？？ PHP7.1.33 Guzzle 6.5

$instance = Builder::factory([

    'mchid'      => $merchantId,

    'serial'     => $merchantCertificateSerial,

    'privateKey' => $merchantPrivateKeyInstance,

    'certs'      => [

        $platformCertificateSerial => $platformPublicKeyInstance,

    ],

]);