WPF - navigating to a frame in multiple ways causes error

Question

I have a WPF window and a frame within the window that contains most of my content. In some cases, I will navigate directly to a URL with the frame and this will cause my frame.Currentsource to populate properly. However, in other cases, I will create a page object and then put the object directly in the frame.Navigate method but this will cause my frame.Currentsource to resolve to a NULL.

How can I make sure that my frame will always have a valid frame.Currentsource value?