DialogFlow v2 fulfillmentMessages

Question

我试图用新闻卡回复用户，但据我所知，如果我按照你的例子说它不起作用。 如果我只是回复这样的履行消息

res.json({
    "fulfillmentMessages": [
      {
        "card": {
          "title": "card title",
          "subtitle": "card text",
          "imageUri": "https://assistant.google.com/static/images/molecule/Molecule-Formation-stop.png",
          "buttons": [
            {
              "text": "button text",
              "postback": "https://assistant.google.com/"
            }
          ]
        }
      }
    ],
    "source": "example.com"
});

我收到此错误：

{
  "responseMetadata": {
    "status": {
      "code": 13,
      "message": "Failed to parse Dialogflow response into AppResponse because of empty speech response",
      "details": [
        {
          "@type": "type.googleapis.com/google.protobuf.Value",
          "value": "{\"id\":\"ef8154ae-96ff-4837-b7e7-d3388223240d\",\"timestamp\":\"2018-04-27T15:19:19.449Z\",\"lang\":\"en-us\",\"result\":{},\"status\":{\"code\":200,\"errorType\":\"success\"},\"sessionId\":\"1524841118917\"}"
        }
      ]
    }
  }
}

如果我添加fulfillmentText（应该是可选的），Google智能助理只会使用纯文本作为回复，并且不会使用卡片。

有人解决了这个问题吗？