
**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.
return <div />;
      }
    }
    const shallowRenderer = createRenderer();
    shallowRenderer.render(<SomeComponent foo={1} />);
    
    
    expect(logs).toEqual(['componentWillMount']);
    logs.splice(0);
    const instance = shallowRenderer.getMountedInstance();
    instance.setState({});
    expect(logs).toEqual(['shouldComponentUpdate', 'componentWillUpdate']);
    logs.splice(0);
    shallowRenderer.render(<SomeComponent foo={2} />);
    
    expect(logs).toEqual([
      'componentWillReceiveProps',
      'shouldComponentUpdate',
      'componentWillUpdate',
    ]);
  });
  it('should only render 1 level deep', () => {
    function Parent() {
      return (
        <div>
          <Child />
        </div>
      );
    }
    function Child() {