Fix kotlin nullable errors in Settings

Fix kotlin nullable errors that were exposed by setting the retention
of android.annotation.NonNull and android.annotation.Nullable to
class retention.

Bug: 294110802
Test: builds
Change-Id: I6aa0516fa4f6443b6d4dff873baf3b08ff9189f0
Merged-In: I6aa0516fa4f6443b6d4dff873baf3b08ff9189f0