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

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

Change-Id: If4e064b3907ed953c8947c5aeed8762cc6db1609
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>