Merge "Revert^2 "Prevent unspecified values in soong_config_string_variable"""...

Merge "Revert^2 "Prevent unspecified values in soong_config_string_variable""" am: c1c91c94 am: f2e3d9b8 am: 9c51d93b

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2056528



Change-Id: I81f45eb51f38815eab69184cbb792e4dfa147464
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>