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

ReactInstrumentation.debugTool.onEndLifeCycleTimer(
          this._debugID,
          'render'
        );
      }
    }
    if (__DEV__) {
      
      if (renderedComponent === undefined &&
          inst.render._isMockFunction) {
        
        
        renderedComponent = null;
      }
    }
    return renderedComponent;
  },
  /**
   * @private
   */
  _renderValidatedComponent: function() {
    var renderedComponent;
    if (__DEV__ || !(this._instance instanceof StatelessComponent)) {
      ReactCurrentOwner.current = this;
      try {
        renderedComponent =
          this._renderValidatedComponentWithoutOwnerOrContext();
      } finally {
        ReactCurrentOwner.current = null;
      }