
**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.
);
    expect(componentDidUpdateParams).toEqual([]);
    expect(componentWillReceivePropsParams).toEqual([]);
    expect(componentWillUpdateParams).toEqual([]);
    expect(setStateParams).toEqual([]);
    expect(shouldComponentUpdateParams).toEqual([]);
    
    shallowRenderer.render(
      React.createElement(SimpleComponent, updatedProp),
      updatedContext,
    );
    expect(componentWillReceivePropsParams).toEqual([
      updatedProp,
      updatedContext,
    ]);
    expect(setStateParams).toEqual([initialState, initialProp]);
    expect(shouldComponentUpdateParams).toEqual([
      updatedProp,
      updatedState,
      updatedContext,
    ]);
    expect(componentWillUpdateParams).toEqual([
      updatedProp,
      updatedState,
      updatedContext,
    ]);
    expect(componentDidUpdateParams).toEqual([]);
  });
  it('can shallowly render components with ref as function', () => {
    class SimpleComponent extends React.Component {