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)

expect(childRenderCount).toBe(1);
    ReactUpdates.batchedUpdates(function() {
      instance.refs.child.setState({x: 1});
    });
    expect(parentRenderCount).toBe(1);
    expect(childRenderCount).toBe(2);
  });
  it('should not reconcile children passed via props', function() {
    var numMiddleRenders = 0;
    var numBottomRenders = 0;
    var Top = React.createClass({
      render: function() {
        return <Middle><Bottom /></Middle>;
      },
    });
    var Middle = React.createClass({
      componentDidMount: function() {
        this.forceUpdate();
      },
      render: function() {
        numMiddleRenders++;
        return React.Children.only(this.props.children);
      },
    });
    var Bottom = React.createClass({
      render: function() {
        numBottomRenders++;
        return null;
      },
    });