Summary:
Alas, it has to be config-gated for now, because a number of core tests depended on the empty-destination update behavior (which is sophisticated).
I'll send a followup diff to remove them.
Reviewed By: kulshrax
Differential Revision: D10376546
fbshipit-source-id: 2ac79e03a91551f96cf8e743c0ee9719557c4fbe
