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.

topMouseOver: 'mouseover',
  topMouseUp: 'mouseup',
  topPaste: 'paste',
  topPause: 'pause',
  topPlay: 'play',
  topPlaying: 'playing',
  topProgress: 'progress',
  topRateChange: 'ratechange',
  topScroll: 'scroll',
  topSeeked: 'seeked',
  topSeeking: 'seeking',
  topSelectionChange: 'selectionchange',
  topStalled: 'stalled',
  topSuspend: 'suspend',
  topTextInput: 'textInput',
  topTimeUpdate: 'timeupdate',
  topTouchCancel: 'touchcancel',
  topTouchEnd: 'touchend',
  topTouchMove: 'touchmove',
  topTouchStart: 'touchstart',
  topTransitionEnd: getVendorPrefixedEventName('transitionend') || 'transitionend',
  topVolumeChange: 'volumechange',
  topWaiting: 'waiting',
  topWheel: 'wheel',
};
/**
 * To ensure no conflicts with other potential React instances on the page
 */
var topListenersIDKey = '_reactListenersID' + String(Math.random()).slice(2);
function getListeningForDocument(mountAt) {