title: Cannot read property 'value' of undefined" on dojo/request/iframe post
body: <p>I have an image upload function that uploads form with image like this:</p>
  
  <pre><code>iframe(url, {
      form: dom.byId("myform"),
      handleAs: "json",
      timeout: 5000,
      method: "POST"
  }).then(function () {
      console.log("Success");
  }, function (Err) {
      console.log(Err);
  });
  </code></pre>
  
  <p>On server side I get the image, but on client side I get TypeError: Cannot read property 'value' of undefined↵    at I [as handleResponse] (<a href="http://ajax.googleapis.com/ajax/libs/dojo/1.9.2/dojo/request/iframe.js:9:114" rel="nofollow">http://ajax.googleapis.com/ajax/libs/dojo/1.9.2/dojo/request/iframe.js:9:114</a>)↵    at r (<a href="http://ajax.googleapis.com/ajax/libs/dojo/1.9.2/dojo/dojo.js:206:81" rel="nofollow">http://ajax.googleapis.com/ajax/libs/dojo/1.9.2/dojo/dojo.js:206:81</a>)". I have no returned value! I do not get what causing the error!
  Please help!</p>