wx.addCard 非指定code时。前端调用报参数错误

wx.addCard({
  cardList: [
    {
      cardId: 'xxx',
      cardExt: '{"openid": "xx", "timestamp": "123", "signature":"xxx"}'
    }
  ],
  success (res) {
    console.log(res.cardList) // 卡券添加结果
  }
})

这样写有问题吗