https://jsfiddle.net/3apqnhmw/

```jsx
class Foo extends React.Component {
  render() {
     return <div>Foo</div>
  }
}

class App extends React.Component {
  render() {
    return Foo
  }
}
```

When `App` returns `Foo` instead of `<Foo />` accidentally, Fiber does not catch this.
expect(normalizeCodeLocInfo(ex.message)).toBe(
      'Objects are not valid as a React child (found: object with keys ' +
        '{x, y, z}). If you meant to render a collection of children, use ' +
        'an array instead.' +
        
        (ReactDOMFeatureFlags.useFiber ? '\n    in div (at **)' : ''),
    );
  });
  it('throws if a plain object even if it is in an owner', () => {
    class Foo extends React.Component {
      render() {
        var children = {
          a: <span />,
          b: <span />,
          c: <span />,
        };
        return <div>{[children]}</div>;
      }
    }
    var container = document.createElement('div');
    var ex;
    try {
      ReactDOM.render(<Foo />, container);
    } catch (e) {
      ex = e;
    }
    expect(ex).toBeDefined();
    expect(normalizeCodeLocInfo(ex.message)).toBe(
      'Objects are not valid as a React child (found: object with keys ' +
        '{a, b, c}). If you meant to render a collection of children, use ' +