https://bugzilla.xamarin.com/show_bug.cgi?id=44399
We did not fully support passing null to name and objectToObserve in
CFNotificationCenter::AddObserver an ArgumentNullException was thrown
The use case of sending null to both name and objectToObserve is to
observe all notifications posted to the notification center, this
won't work using darwing notification center, it is restricted
by apple.
Alex Soto
Rolf Bjarne Kvinge