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)

return {tabKey: 'hello'};
      },
      render: function() {
        var child = this.props.children;
        return (
          <Box ref="box">
            <div
              ref="switcherDiv"
              style={{
                display: this.state.tabKey === child.key ? '' : 'none',
              }}>
              {child}
            </div>
          </Box>
        );
      },
    });
    var App = React.createClass({
      mixins: [UpdateLoggingMixin],
      render: function() {
        return (
          <Switcher ref="switcher">
            <Child key="hello" ref="child" />
          </Switcher>
        );
      },
    });
    var root = <App />;
    root = ReactTestUtils.renderIntoDocument(root);
    function expectUpdates(desiredWillUpdates, desiredDidUpdates) {