Given the following test case

``` jsx
function TestCmp() {
  return <span>{NaN}</span>;
}

ReactDOM.render(<TestCmp />, document.getElementById('app'));
```

Produces the following warning:

```
Warning: Component's children should not be mutated.
    in span (created by TestCmp)
    in TestCmp (created by Unknown)
```

This is probably caused by [this mutation check](https://github.com/facebook/react/blob/328fc75bc910032ff37dc9d93429fb14b476bd0d/src/renderers/shared/hooks/ReactChildrenMutationWarningHook.js#L34), which was introduced in 15.3.0, but it doesn't work for NaN, because NaN != NaN

ReactDOM.unmountComponentAtNode(element);
      expect(element.innerHTML).toEqual('');
      ReactDOM.render(<TestComponent name="x" />, element);
      expect(mountCount).toEqual(2);
      expect(element.innerHTML).not.toEqual(lastMarkup);
      
      
      
      
      ReactDOM.unmountComponentAtNode(element);
      expect(element.innerHTML).toEqual('');
      ExecutionEnvironment.canUseDOM = false;
      lastMarkup = ReactServerRendering.renderToString(
        <TestComponent name="x" />
      );
      ExecutionEnvironment.canUseDOM = true;
      element.innerHTML = lastMarkup;
      var instance = ReactDOM.render(<TestComponent name="x" />, element);
      expect(mountCount).toEqual(3);
      expect(element.innerHTML).toBe(lastMarkup);
      
      expect(numClicks).toEqual(0);
      ReactTestUtils.Simulate.click(ReactDOM.findDOMNode(instance.refs.span));
      expect(numClicks).toEqual(1);
      ReactDOM.unmountComponentAtNode(element);
      expect(element.innerHTML).toEqual('');
      
      
      element.innerHTML = lastMarkup;