Merge "Make clear_var_list set nonexistant variables to empty strings" am:...

Merge "Make clear_var_list set nonexistant variables to empty strings" am: 8998fd72 am: e2e127b2

Original change: https://android-review.googlesource.com/c/platform/build/+/2351362



Change-Id: I56835cccc5dee6ddcea19122a5b69ee112ee5510
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>