<!--
  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

constructor(props) {
        super(props);
        this.state = {error: false};
      }
      render() {
        log.push('Boundary render');
        if (!this.state.error) {
          return (
            <div>
              <button onClick={this.onClick}>ClickMe</button>
              <Angry />
            </div>
          );
        } else {
          return <div>Happy Birthday!</div>;
        }
      }
      componentDidMount() {
        log.push('Boundary componentDidMount');
      }
      componentWillUnmount() {
        log.push('Boundary componentWillUnmount');
      }
      onClick() {