Re: [PATCH v4 15/16] refs.c: remove fallback-to-main-store code get_submodule_ref_store()

> At this state, there are three get_submodule_ref_store() callers:
> 
>  - for_each_remote_ref_submodule()
>  - handle_revision_pseudo_opt()
>  - resolve_gitlink_ref()
> 
> The first two deal explicitly with submodules (and we should never fall
> back to the main ref store as a result). They are only called from
> submodule.c:
> 
>  - find_first_merges()
>  - submodule_needs_pushing()
>  - push_submodule()
> 
> The last one, as its name implies, deals only with submodules too, and
> the "submodule" (path) argument must be a non-NULL, non-empty string.
> 
> So, this "if NULL or empty string" code block should never ever
> trigger. And it's wrong to fall back to the main ref store
> anyway. Delete it.