The code

``` javascript
class Comp extends React.Component {
  componentWillMount() {
    setTimeout(() => {
      this.setState({});
    });
  }

  render() {
    return <div onClick={() => {}} />;
  }
}

ReactDOMServer.renderToString(<Comp />);
```

produces errors:

> Warning: React can't find the root component node for data-reactid value `.0`. If you're seeing this message, it probably means that you've loaded two copies of React on the page. At this time, only a single copy of React can be loaded at a time.
> 
> Uncaught TypeError: Cannot read property 'firstChild' of undefined

But if I remove `onClick` handler the errors go away...

See demo: http://codepen.io/dened/pen/YyByYr

* @final
   */
  isMounted: function(publicInstance) {
    return false;
  },
  /**
   * Enqueue a callback that will be executed after all the pending updates
   * have processed.
   *
   * @param {ReactClass} publicInstance The instance to use as `this` context.
   * @param {?function} callback Called after state is updated.
   * @internal
   */
  enqueueCallback: function(publicInstance, callback) { },
  /**
   * Forces an update. This should only be invoked when it is known with
   * certainty that we are **not** in a DOM transaction.
   *
   * You may want to call this when you know that some deeper aspect of the
   * component's state has changed but `setState` was not called.
   *
   * This will not invoke `shouldComponentUpdate`, but it will invoke
   * `componentWillUpdate` and `componentDidUpdate`.
   *
   * @param {ReactClass} publicInstance The instance that should rerender.
   * @internal
   */
  enqueueForceUpdate: function(publicInstance) {
    warnTDZ(publicInstance, 'forceUpdate');
  },