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.
priority,
      );
      created.return = returnFiber;
      return created;
    }
    if (typeof newChild === 'object' && newChild !== null) {
      switch (newChild.$$typeof) {
        case REACT_ELEMENT_TYPE: {
          const created = createFiberFromElement(
            newChild,
            returnFiber.internalContextTag,
            priority,
          );
          created.ref = coerceRef(null, newChild);
          created.return = returnFiber;
          return created;
        }
        case REACT_COROUTINE_TYPE: {
          const created = createFiberFromCoroutine(
            newChild,
            returnFiber.internalContextTag,
            priority,
          );
          created.return = returnFiber;
          return created;
        }
        case REACT_YIELD_TYPE: {
          const created = createFiberFromYield(
            newChild,
            returnFiber.internalContextTag,