**Do you want to request a *feature* or report a *bug*?**

bug

**What is the current behavior?**

The warning for a failure to initialize state when using `getDerivedStateFromProps` is not as clear as it could be.

This component produces the warning:
> MyComponent: Did not properly initialize state during construction. Expected state to be an object, but it was undefined.`

```js
class MyComponent extends React.Component {
  static getDerivedStateFromProps(nextProps, prevState) {
    return null;
  }
  render() {
    return <span>Foo</span>
  }
}
```

The warning can be resolved by adding `state = {}` either in the class definition or the constructor, or by not using `getDerivedStateFromProps`.

See https://github.com/reactjs/reactjs.org/issues/796 for more detail on why this warning message can be counter-intuitive.

Since the [warning is specific](https://github.com/facebook/react/blob/b548b3cd640dbd515f5d67dafc0216bb7ee0d796/packages/react-reconciler/src/ReactFiberClassComponent.js#L509-L510) to the use of `getDerivedStateFromProps` and not triggered by any other state or lifecycle methods, and state initialization isn't required for other state methods like `this.setState`, it would make sense to me to mention `getDerivedStateFromProps` explicitly in the warning.

Here's a proposal for a new warning message:
> MyComponent: Component state must be initialized when using getDerivedStateFromProps. Expected state to be an object, but it was undefined.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React >= 16.3.0

'property to define propTypes instead.',
      name,
    );
    const noInstanceContextTypes = !instance.contextTypes;
    warningWithoutStack(
      noInstanceContextTypes,
      'contextTypes was defined as an instance property on %s. Use a static ' +
        'property to define contextTypes instead.',
      name,
    );
    const noComponentShouldUpdate =
      typeof instance.componentShouldUpdate !== 'function';
    warningWithoutStack(
      noComponentShouldUpdate,
      '%s has a method called ' +
        'componentShouldUpdate(). Did you mean shouldComponentUpdate()? ' +
        'The name is phrased as a question because the function is ' +
        'expected to return a value.',
      name,
    );
    if (
      type.prototype &&
      type.prototype.isPureReactComponent &&
      typeof instance.shouldComponentUpdate !== 'undefined'
    ) {
      warningWithoutStack(
        false,
        '%s has a method called shouldComponentUpdate(). ' +
          'shouldComponentUpdate should not be used when extending React.PureComponent. ' +
          'Please extend React.Component if shouldComponentUpdate is used.',