By having our app wrapped with Sentry (error catching service) we've encountered a bug - which may not be React specific but some kind of a workaround for it should be done. With that in mind I'm not sure how to tackle it yet.

https://github.com/facebook/react/blob/1573baaee8ba1c9cd84145b01effcb5eb80503fb/src/renderers/dom/client/ReactBrowserEventEmitter.js#L363

`TypeError: Cannot use 'in' operator to search for 'pageX' in null` - which occurs during mounting a root component into the DOM (using React 15)

It happens really rarely in Chrome (so far caught only there, on versions 49 and 50, both Mac and Windows). With thousands renders of our app daily we got only 7 such hits in the past 3 days.

I've tried to search any info how `document.createEvent('MouseEvent')` can return `null`, but couldn't find any viable info.

With React's popularity is odd too me that nobody has filled this issue earlier which leds me to think that maybe our usage is somehow different than others and the only thing 'kinda' special is that our app is running inside an iframe.

);
  },
  /**
   * We listen for bubbled touch events on the document object.
   *
   * Firefox v8.01 (and possibly others) exhibited strange behavior when
   * mounting `onmousemove` events at some node that was not the document
   * element. The symptoms were that if your mouse is not moving over something
   * contained within that mount point (for example on the background) the
   * top-level listeners for `onmousemove` won't be called. However, if you
   * register the `mousemove` on the document object, then it will of course
   * catch all `mousemove`s. This along with iOS quirks, justifies restricting
   * top-level listeners to the document object only, at least for these
   * movement types of events and possibly all events.
   *
   * @see http://www.quirksmode.org/blog/archives/2010/09/click_event_del.html
   *
   * Also, `keyup`/`keypress`/`keydown` do not bubble to the window on IE, but
   * they bubble to document.
   *
   * @param {string} registrationName Name of listener (e.g. `onClick`).
   * @param {object} contentDocumentHandle Document which owns the container
   */
  listenTo: function(registrationName, contentDocumentHandle) {
    var mountAt = contentDocumentHandle;
    var isListening = getListeningForDocument(mountAt);
    var dependencies =
      EventPluginRegistry.registrationNameDependencies[registrationName];
    for (var i = 0; i < dependencies.length; i++) {
      var dependency = dependencies[i];