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

var warnAboutAccessingKey = function() {
    if (!specialPropKeyWarningShown) {
      specialPropKeyWarningShown = true;
      warning(
        false,
        '%s: `key` is not a prop. Trying to access it will result ' +
        'in `undefined` being returned. If you need to access the same ' +
        'value within the child component, you should pass it as a different ' +
        'prop. (https://fb.me/react-special-props)',
        displayName
      );
    }
  };
  warnAboutAccessingKey.isReactWarning = true;
  Object.defineProperty(props, 'key', {
    get: warnAboutAccessingKey,
    configurable: true,
  });
}
function defineRefPropWarningGetter(props, displayName) {
  var warnAboutAccessingRef = function() {
    if (!specialPropRefWarningShown) {
      specialPropRefWarningShown = true;
      warning(
        false,
        '%s: `ref` is not a prop. Trying to access it will result ' +