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

}
    return markup;
  },
  getHostNode: function() {
    return ReactReconciler.getHostNode(this._renderedComponent);
  },
  /**
   * Releases any resources allocated by `mountComponent`.
   *
   * @final
   * @internal
   */
  unmountComponent: function(safely) {
    if (!this._renderedComponent) {
      return;
    }
    var inst = this._instance;
    if (inst.componentWillUnmount && !inst._calledComponentWillUnmount) {
      inst._calledComponentWillUnmount = true;
      if (__DEV__) {
        if (this._debugID !== 0) {
          ReactInstrumentation.debugTool.onBeginLifeCycleTimer(
            this._debugID,
            'componentWillUnmount'
          );
        }
      }
      if (safely) {
        var name = this.getName() + '.componentWillUnmount()';
        ReactErrorUtils.invokeGuardedCallback(name, inst.componentWillUnmount.bind(inst));