NullReferenceException on InitializeComponents - What did I do wrong?

Hello,

I've encountered an error when loading a new ContentPage. When the app reaches InitializeComponents() I'm thrown with System.NullReferenceException. (both on iOS and Android)

Can someone please explain what I did wrong here?

Here's the code and stack trace: (I used PasteBin because they're long)
SettingsPage.xaml
SettingsPage.xaml.cs
Stack Trace

Thanks in advance for any help!