React 0.14.8
We see this in browser tests but never manually triggered, so bug is seemingly timing sensitive.

```
Uncaught TypeError: Cannot read property 'classList' of null CSSCore.js:38
CSSCore.addClass @ CSSCore.js:38
React.createClass.flushClassNameQueue @ ReactCSSTransitionGroupChild.js:116
```

`component.isMounted()` is `true`, but in these cases `ReactDOM.findDOMNode(this)` then returns null here
https://github.com/facebook/react/blob/master/src/addons/transitions/ReactCSSTransitionGroupChild.js#L116

displayName: 'ReactCSSTransitionGroupChild',
  propTypes: {
    name: React.PropTypes.oneOfType([
      React.PropTypes.string,
      React.PropTypes.shape({
        enter: React.PropTypes.string,
        leave: React.PropTypes.string,
        active: React.PropTypes.string,
      }),
      React.PropTypes.shape({
        enter: React.PropTypes.string,
        enterActive: React.PropTypes.string,
        leave: React.PropTypes.string,
        leaveActive: React.PropTypes.string,
        appear: React.PropTypes.string,
        appearActive: React.PropTypes.string,
      }),
    ]).isRequired,
    
    
    
    appear: React.PropTypes.bool,
    enter: React.PropTypes.bool,
    leave: React.PropTypes.bool,
    appearTimeout: React.PropTypes.number,
    enterTimeout: React.PropTypes.number,
    leaveTimeout: React.PropTypes.number,
  },
  transition: function(animationType, finishCallback, userSpecifiedDelay) {
    var node = ReactDOM.findDOMNode(this);