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

if (__DEV__) {
    warning(
      false,
      '%s(...): Can only update a mounted or mounting component. ' +
      'This usually means you called %s() on an unmounted component. ' +
      'This is a no-op. Please check the code for the %s component.',
      callerName,
      callerName,
      publicInstance.constructor && publicInstance.constructor.displayName || ''
    );
  }
}
/**
 * This is the abstract API for an update queue.
 */
var ReactNoopUpdateQueue = {
  /**
   * Checks whether or not this composite component is mounted.
   * @param {ReactClass} publicInstance The instance we want to test.
   * @return {boolean} True if mounted, false otherwise.
   * @protected