[automerger skipped] Fixes more  @Nullable issues in System UI and WMShell. am: 63a020ccfb am: 61a1898935 -s ours

am skip reason: Merged-In Ibd2b0163b47571da5f276f09ce5dcfd875f09a1c with SHA-1 d4e6575948 is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24588595

Change-Id: I210403bd8501fdc1bdedbdb28a58878ace22c3fb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>