Modal Popup not showing Navigation Bar

Hi,

Referring to this thread:

https://forums.xamarin.com/discussion/comment/370580#Comment_370580

when I changed from:

Navigation.PushModalAsync(new NavigationPage(new Signin())
{
    BarBackgroundColor = Color.White,
    BarTextColor = Color.Black
});

to:

await Navigation.PushModalAsync(new Signin());

now the popup is not showing the title bar

How can I fix this please?

Thanks,
Jassim