Navigation.push async from inside a detail Page

Hii, I have a master detail page in xamarin.forms project.
inside the detail page i have a button that must redirect me to another page. navigation.push.async is not working it give a null exception.

in my app.cs I have :
Current.MainPage = new RootPage { Detail = new NavigationPage(new HomePage()) };

(RootPage is my master and HomePage is the detail)
from HomePage I need to pushasync another detail Page... How to do this??

I know I can use new RootPage { Detail = new NavigationPage(new SettingsPage()) }; but i don't need to reset the navigation stack..

Thank you for your Help.