title: Malformed Response 'final_response' must be set
body: <p>I'm using DialogFlow's webhook thing and when I send my JSON response as follows:</p>
  
  <pre><code>{
    "fulfillmentText": "This is a text response",
    "source": "example.com",
    "payload": {
      "google": {
        "richResponse": {
          "items": [
            {
              "simpleResponse": {
                "textToSpeech": "this is a simple response"
              }
            }
          ]
        }
      }
    }
  }
  </code></pre>
  
  <p>but I get the error <code>MalformedResponse 'final_response' must be set.</code> after the webserver responds.</p>