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.

/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ReactBrowserEventEmitter
 */
'use strict';
var EventPluginRegistry = require('EventPluginRegistry');
var ReactEventEmitterMixin = require('ReactEventEmitterMixin');
var ViewportMetrics = require('ViewportMetrics');
var getVendorPrefixedEventName = require('getVendorPrefixedEventName');
var isEventSupported = require('isEventSupported');
/**
 * Summary of `ReactBrowserEventEmitter` event handling:
 *
 *  - Top-level delegation is used to trap most native browser events. This
 *    may only occur in the main thread and is the responsibility of
 *    ReactEventListener, which is injected and can therefore support pluggable
 *    event sources. This is the only work that occurs in the main thread.
 *
 *  - We normalize and de-duplicate events to account for browser quirks. This