<!--
  Note: if the issue is about documentation or the website, please file it at:
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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

return <a role="link" />;
    }
    const renderer = ReactTestRenderer.create(<Link />);
    expect(renderer.toJSON()).toEqual({
      type: 'a',
      props: {role: 'link'},
      children: null,
    });
  });
  it('renders a top-level empty component', () => {
    function Empty() {