Am 24.05.23 um 21:51 schrieb Taylor Blau:

There is no need to check whether `sub`
itself is NULL, since we already perform this check earlier in
`prepare_to_clone_next_submodule()`.

Right, and if "sub" is NULL then next_submodule_warn_missing() is called
and prepare_to_clone_next_submodule() is exited early.

By adding a NULL-ness check on `sub->url`, we'll fall into the 'else'
branch, setting `url` to `sub->url` (which is NULL). Before attempting
to invoke `git submodule--helper clone`, check whether `url` is NULL,
and die() if it is.

Why die() here instead of just warn and skip as well?

René