State initialization disparity between shallow renderer and ReactDOM

[jwbay]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
The shallow renderer defaults a class component's state to empty object if it's not set. "Real" renderers don't seem to do this, so a component can render successfully in the shallow renderer, but fail at runtime in the browser with a null reference error.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem.
Here is ReactDOM's behavior (crashes reading an uninitialized state value): https://codesandbox.io/s/4jv82zmp0
Here is the shallow renderer behavior (component able to render): https://codesandbox.io/s/pp733nrxzq

What is the expected behavior?
They initialize state in the same way.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
React 16. This wasn't an issue in React 15.

[gaearon]

This is a bug in the shallow renderer. Want to send a fix?