Fixes @Nullable issues SystemUI-tests am: b9b9aa5eb6

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24592301

Change-Id: Iea3f1bcf0663a35a7cb238e3c48f6f26e7c46141
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>