
**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.
throw Error('This component should not render');
    }
    const shallowRenderer = createRenderer();
    shallowRenderer.render(React.createElement(Parent));
  });
  it('should have shallow rendering', () => {
    class SomeComponent extends React.Component {
      render() {
        return (
          <div>
            <span className="child1" />
            <span className="child2" />
          </div>
        );
      }
    }
    const shallowRenderer = createRenderer();
    const result = shallowRenderer.render(<SomeComponent />);
    expect(result.type).toBe('div');
    expect(result.props.children).toEqual([
      <span className="child1" />,
      <span className="child2" />,
    ]);
  });
  it('should enable shouldComponentUpdate to prevent a re-render', () => {
    let renderCounter = 0;
    class SimpleComponent extends React.Component {