Merge "unregistered null callback will cause a crash later" am: f4e0f096b5 am: 645d524fba

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2372391

Change-Id: I44beeb193041c47c3b98c3c1a10ecb195511dd97
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>