CreateViewController Errors after Migrating to Unified API

I am using the latest Xamarin.Forms from Xamarin.Forms 1.4.2.6359 from Nugget.

After updating my code to unified API I am having an issue error in my line of code

Page myPage;

UIWindow window = new UIWindow(UIScreen.MainScreen.Bounds);
window.RootViewController = myPage.CreateViewController();

Here is the error.
And error Cannot implicitly convert type 'MonoTouch.UIKit.UIViewController' to 'UIKit.UIViewController'