Add more consistent null checks

This change moves the null check into the service implementation. Since
exceptions on oneway binder interfaces are ignored (across process), the
code was changed to just return early instead.

This also adds a couple of Objects.requireNonNull() assertions in
TetheringManager to assert the existing @NonNull annotation.

Test: TH
Bug: 337167681
Change-Id: I5301ed084bb26c2f910041e9b25314f8181718d1
3 files changed