Merge "Fix @Nullability mismatch with PipTransition" into udc-qpr-dev am: f62a0e11d6

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24263643

Change-Id: Ifd21e3ce70eec1ce23960867af17cd70c1d279b1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>