Old code, new Xcode

When you download some old code from the Interwebs with such like:

[self.window addSubview:self.viewController.view];

and it runs just fine... and later you update Xcode and start getting runtime errors:

Applications are expected to have a root view controller at the end of application launch

Fortunately the fix is easy:

[self.window setRootViewController:self.viewController];

Thanks, Interwebs!!