
**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.
state = {count: 0};
      componentWillReceiveProps(nextProps) {
        if (nextProps.updateState) {
          this.setState({count: 1});
        }
      }
      render() {
        return <div>{this.state.count}</div>;
      }
    }
    const shallowRenderer = createRenderer();
    let result = shallowRenderer.render(
      <SimpleComponent updateState={false} />,
    );
    expect(result.props.children).toEqual(0);
    result = shallowRenderer.render(<SimpleComponent updateState={true} />);
    expect(result.props.children).toEqual(1);
  });
  it('can setState with an updater function', () => {
    let instance;
    class SimpleComponent extends React.Component {