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

render() {
        return <Child><div ref="test" /></Child>;
      }
      componentDidMount() {
        expect(this.refs && this.refs.test).toEqual(undefined);
      }
    }
    class Child extends React.Component {
      render() {
        return <div />;
      }
    }
    var instance = <Parent child={<span />} />;
    instance = ReactTestUtils.renderIntoDocument(instance);
  });
  it('should support new-style refs', () => {
    var innerObj = {};
    var outerObj = {};
    class Wrapper extends React.Component {
      getObject = () => {
        return this.props.object;
      };
      render() {
        return <div>{this.props.children}</div>;
      }
    }
    var mounted = false;
    class Component extends React.Component {