Hello,

After updating to React 15.0.1, we are getting the following error:

```
Uncaught TypeError: Cannot read property 'addEventListener' of null
```

![image](https://cloud.githubusercontent.com/assets/4996164/14602577/5bb4e9f2-0571-11e6-9aa1-98de49f50d76.png)

if (__DEV__) {
    warning(
      element === null || element === false || ReactElement.isValidElement(element),
      '%s(...): A valid React element (or null) must be returned. You may have ' +
      'returned undefined, an array or some other invalid object.',
      Component.displayName || Component.name || 'Component'
    );
  }
}
function invokeComponentDidMountWithTimer() {
  var publicInstance = this._instance;
  if (this._debugID !== 0) {
    ReactInstrumentation.debugTool.onBeginLifeCycleTimer(
      this._debugID,
      'componentDidMount'
    );
  }
  publicInstance.componentDidMount();
  if (this._debugID !== 0) {
    ReactInstrumentation.debugTool.onEndLifeCycleTimer(
      this._debugID,
      'componentDidMount'
    );
  }
}
function invokeComponentDidUpdateWithTimer(prevProps, prevState, prevContext) {