https://codesandbox.io/s/40j50607y0

Rendering a component like:

```js
const Foo = () => <React.Fragment />
```

Throws the error:

> Foo(...): Nothing was returned from render. This usually means a return statement is missing. Or, to render nothing, return null.

The error is confusing because clearly `Foo` _is_ returning a value. I don't know if we want to support rendering empty fragments, but in any case this error is confusing.

If this isn't allowed it should explicitly call out that a component cannot return a fragment with no children.

cc @gaearon 
return {
          foo: this.props.bar,
          getFoo: () => this.props.bar,
        };
      }
      render() {
        return ReactDOM.createPortal(<Component />, portalContainer);
      }
    }
    ReactDOM.render(<Parent bar="initial" />, container);
    expect(portalContainer.innerHTML).toBe('<div>initial-initial</div>');
    expect(container.innerHTML).toBe('');
    ReactDOM.render(<Parent bar="changed" />, container);
    expect(portalContainer.innerHTML).toBe('<div>changed-changed</div>');
    expect(container.innerHTML).toBe('');
  });
  it('findDOMNode should find dom element after expanding a fragment', () => {
    class MyNode extends React.Component {
      render() {
        return !this.props.flag
          ? [<div key="a" />]
          : [<span key="b" />, <div key="a" />];
      }
    }
    const myNodeA = ReactDOM.render(<MyNode />, container);
    const a = ReactDOM.findDOMNode(myNodeA);
    expect(a.tagName).toBe('DIV');
    const myNodeB = ReactDOM.render(<MyNode flag={true} />, container);
    expect(myNodeA === myNodeB).toBe(true);
    const b = ReactDOM.findDOMNode(myNodeB);