<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**Do you want to request a *feature* or report a *bug*?**

bug.

**What is the current behavior?**

```js
  renderer.create(
    <Fragment>
      <Fragment>foo</Fragment>
    </Fragment>
  )
  .toTree()
```

> Invariant Violation: toTree() does not yet know how to handle nodes with tag=10

https://codesandbox.io/s/olky92m01y

**What is the expected behavior?**

returns a tree.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

16.2.0

hostContext: Object,
    internalInstanceHandle: Object,
  ): TextInstance {
    return {
      text,
      tag: 'TEXT',
    };
  },
  scheduleDeferredCallback(fn: Function): number {
    return setTimeout(fn, 0, {timeRemaining: Infinity});
  },
  cancelDeferredCallback(timeoutID: number): void {
    clearTimeout(timeoutID);
  },
  getPublicInstance,
  now(): number {
    
    return 0;
  },
  mutation: {
    commitUpdate(
      instance: Instance,
      updatePayload: {},
      type: string,
      oldProps: Props,
      newProps: Props,
      internalInstanceHandle: Object,
    ): void {
      instance.type = type;
      instance.props = newProps;