Show a meaningful error on missing element

[gaearon]

Can you spot a mistake here?

storiesOf('App', module)
  .add('normal', () => {
    <App />
  });

I used { instead of (, and so didn’t return anything.
As a result, I got this error:

I think Storybook should validate elements before passing them to React. If element is undefined, it should throw something like "Expected the function in storiesOf().add(...) to return a React element. Instead it returned undefined. Did you forget the return statement?"

Similarly, if element.type is undefined, print something like "Expected the function in storiesOf().add(...) to return a valid React element. However, element's type is undefined. If you imported that component without the curly braces, verify that it was exported with an "export default" syntax."

[arunoda]

This is pretty great.
And I think many people would have met with this error.
I can do a fix.

[arunoda]

Fixed with v2.22.0