**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

return null;
        }
      },
      enqueueReplaceState: function(publicInstance, completeState) {
        replace = true;
        queue = [completeState];
      },
      enqueueSetState: function(publicInstance, currentPartialState) {
        if (queue === null) {
          warnNoop(publicInstance, 'setState');
          return null;
        }
        queue.push(currentPartialState);
      },
    };
    let inst;
    if (shouldConstruct(Component)) {
      inst = new Component(element.props, publicContext, updater);
      if (typeof Component.getDerivedStateFromProps === 'function') {
        if (__DEV__) {
          if (inst.state === null || inst.state === undefined) {
            const componentName = getComponentName(Component) || 'Unknown';
            if (!didWarnAboutUninitializedState[componentName]) {
              warningWithoutStack(
                false,
                '%s: Did not properly initialize state during construction. ' +
                  'Expected state to be an object, but it was %s.',
                componentName,
                inst.state === null ? 'null' : 'undefined',
              );