After update to sd-switch 0.5.0, `home-manager switch` failed with the
following error message:
> Error: Error switching
>
> Caused by:
> 0: Failed to build switch plan
> 1: No such file or directory (os error 2)
This was caused by a non-existing target unit directory due to no user
services being managed by home-manager. This change makes sd-switch
run with pkgs.emptyDirectory as the target in such cases.
Closes: https://github.com/nix-community/home-manager/issues/5552
7a88ff6ad1