
**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.
constructor(props, context) {
        super(props, context);
        this.state = initialState;
      }
      componentDidUpdate(...args) {
        componentDidUpdateParams.push(...args);
      }
      componentWillReceiveProps(...args) {
        componentWillReceivePropsParams.push(...args);
        this.setState((...innerArgs) => {
          setStateParams.push(...innerArgs);
          return updatedState;
        });
      }
      componentWillUpdate(...args) {
        componentWillUpdateParams.push(...args);
      }
      shouldComponentUpdate(...args) {
        shouldComponentUpdateParams.push(...args);
        return true;
      }
      render() {
        return null;
      }
    }
    const shallowRenderer = createRenderer();
    
    shallowRenderer.render(
      React.createElement(SimpleComponent, initialProp),
      initialContext,