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 (renderedElement === undefined) {
      renderedElement = this._renderValidatedComponent();
    }
    this._renderedNodeType = ReactNodeTypes.getType(renderedElement);
    var child = this._instantiateReactComponent(
      renderedElement
    );
    this._renderedComponent = child;
    if (__DEV__) {
      if (child._debugID !== 0 && this._debugID !== 0) {
        ReactInstrumentation.debugTool.onSetParent(
          child._debugID,
          this._debugID
        );
      }
    }
    var markup = ReactReconciler.mountComponent(
      child,
      transaction,
      hostParent,
      hostContainerInfo,
      this._processChildContext(context)
    );
    if (__DEV__) {
      if (this._debugID !== 0) {
        ReactInstrumentation.debugTool.onSetChildren(
          this._debugID,
          child._debugID !== 0 ? [child._debugID] : []
        );
      }