
**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.
this._instance.context = context;
    this._instance.props = props;
    this._instance.state = this._instance.state || emptyObject;
    this._instance.updater = this._updater;
    if (typeof this._instance.componentWillMount === 'function') {
      const beforeState = this._newState;
      this._instance.componentWillMount();
      
      if (beforeState !== this._newState) {
        this._instance.state = this._newState || emptyObject;
      }
    }
    this._rendered = this._instance.render();
    
    
  }
  _updateClassComponent(type, props, context) {
    const oldState = this._instance.state || emptyObject;
    const oldProps = this._instance.props;
    if (
      oldProps !== props &&
      typeof this._instance.componentWillReceiveProps === 'function'
    ) {
      this._instance.componentWillReceiveProps(props, context);
    }
    
    const state = this._newState || oldState;