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() {
        log.push(`inner ${this.props.id} render`);
        return <div />;
      }
      componentDidMount() {
        log.push(`inner ${this.props.id} componentDidMount`);
      }
      componentDidUpdate() {
        log.push(`inner ${this.props.id} componentDidUpdate`);
      }
      componentWillUnmount() {
        log.push(`inner ${this.props.id} componentWillUnmount`);
      }
    }
    class Outer extends React.Component {