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

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */
import type {Fiber} from 'react-reconciler/src/ReactFiber';
import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
import ReactFiberReconciler from 'react-reconciler';
import {batchedUpdates} from 'events/ReactGenericBatching';
import {findCurrentFiberUsingSlowPath} from 'react-reconciler/reflection';
import emptyObject from 'fbjs/lib/emptyObject';
import {
  Fragment,
  FunctionalComponent,
  ClassComponent,
  HostComponent,
  HostText,
  HostRoot,
} from 'shared/ReactTypeOfWork';
import invariant from 'fbjs/lib/invariant';
type TestRendererOptions = {
  createNodeMock: (element: React$Element<any>) => any,
};
type ReactTestRendererJSON = {|
  type: string,