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 
}
  }
  function createChild(
    returnFiber: Fiber,
    newChild: any,
    expirationTime: ExpirationTime,
  ): Fiber | null {
    if (typeof newChild === 'string' || typeof newChild === 'number') {
      /
      /
      /
      const created = createFiberFromText(
        '' + newChild,
        returnFiber.mode,
        expirationTime,
      );
      created.return = returnFiber;
      return created;
    }
    if (typeof newChild === 'object' && newChild !== null) {
      switch (newChild.$$typeof) {
        case REACT_ELEMENT_TYPE: {
          const created = createFiberFromElement(
            newChild,
            returnFiber.mode,
            expirationTime,
          );
          created.ref = coerceRef(returnFiber, null, newChild);
          created.return = returnFiber;
          return created;