I was just about to merge this but, after further thought, it seems to me we shouldn't remove (or perhaps even deprecate) this property.

This property really means "treat an empty string the same as null" (which would then either be rejected or accepted based on requires-reply).

Maybe instead of turning it into a no-op, we should retain the functionality with a warning that it will be removed later.

Or, maybe rename it "empty-result-is-null"  ??? 

cc @markfisher since he raised the original question