e0e65cbf8e
This hopefully fixes a regression introduced by 08b214a. In bf129a2, it was already fixed for normal uid/gid values and it got reintroduced by sub-uid/gid-handling again, so I've refactored it a bit into a filterNull function which takes care of also the filtering introduced by bf129a2. I have not tested this extensively, but master is already broken for systems with `mutableUsers = true` and no uid values set. Signed-off-by: aszlig <aszlig@redmoonstudios.org>