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 
render() {
        return <div onClick={false} />;
      }
    }
    expect(() => ReactDOM.render(<Example />, container)).toWarnDev(
      'Expected `onClick` listener to be a function, instead got `false`.\n\n' +
        'If you used to conditionally omit it with onClick={condition && value}, ' +
        'pass onClick={condition ? value : undefined} instead.\n',
      '    in div (at **)\n' + '    in Example (at **)',
    );
  });
  it('should not update event handlers until commit', () => {
    let ops = [];
    const handlerA = () => ops.push('A');
    const handlerB = () => ops.push('B');
    class Example extends React.Component {
      state = {flip: false, count: 0};
      flip() {
        this.setState({flip: true, count: this.state.count + 1});
      }
      tick() {
        this.setState({count: this.state.count + 1});
      }
      render() {
        const useB = !this.props.forceA && this.state.flip;
        return <div onClick={useB ? handlerB : handlerA} />;
      }
    }
    class Click extends React.Component {