
**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.
static contextTypes = {
        foo: PropTypes.string,
      };
      state = {
        bar: 'bar',
      };
      render() {
        return <div>{`${this.context.foo}:${this.state.bar}`}</div>;
      }
    }
    const shallowRenderer = createRenderer();
    let result = shallowRenderer.render(<SimpleComponent />, {
      foo: 'foo',
    });
    expect(result).toEqual(<div>foo:bar</div>);
    const instance = shallowRenderer.getMountedInstance();
    instance.setState({bar: 'baz'});
    result = shallowRenderer.getRenderOutput();
    expect(result).toEqual(<div>foo:baz</div>);
  });
  it('can fail context when shallowly rendering', () => {
    class SimpleComponent extends React.Component {
      static contextTypes = {
        name: PropTypes.string.isRequired,
      };
      render() {