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(child.state.y).toBe(0);
      expect(parentUpdateCount).toBe(0);
      expect(childUpdateCount).toBe(0);
    });
    expect(instance.state.x).toBe(1);
    expect(child.state.y).toBe(2);
    expect(parentUpdateCount).toBe(1);
    expect(childUpdateCount).toBe(1);
  });
  it('should batch child/parent state updates together', function() {
    var parentUpdateCount = 0;
    var Parent = React.createClass({
      getInitialState: function() {
        return {x: 0};
      },
      componentDidUpdate: function() {
        parentUpdateCount++;
      },
      render: function() {
        return <div><Child ref="child" x={this.state.x} /></div>;
      },
    });
    var childUpdateCount = 0;
    var Child = React.createClass({
      getInitialState: function() {
        return {y: 0};
      },
      componentDidUpdate: function() {
        childUpdateCount++;
      },