Merge "Revert "Revert "[AC] Fix NPE. If the client sends multiple unregister...

Merge "Revert "Revert "[AC] Fix NPE. If the client sends multiple unregister requests at the same time, the client request could be null before the next request is processed.""" into udc-dev am: f415752b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/23100716



Change-Id: I99abf9baf8387ff46ee516b9eb5ec0c122663d29
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>