[automerger skipped] Support optional prop assignments am: 598ea498 am:...

[automerger skipped] Support optional prop assignments am: 598ea498 am: 10929231 am: 821feea0 -s ours

am skip reason: Change-Id I9c073a21c8257987cf2378012cadaeeeb698a4fb with SHA-1 7aeb8de7 is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/+/12042306

Change-Id: I905befb8614472f0cc448a05af8e77c06bed389e