In systems without initrd (e.g. containers) that also use system.replaceDependencies, we'd get:
error: attribute 'initialRamdisk' missing
at /nix/store/8vfhnwmmzqqzy97q9c5m4bzyaqqf63zy-source/nixos/modules/system/activation/top-level.nix:286:21:
285| cutoffPackages = mkOption {
286| default = [ config.system.build.initialRamdisk ];
| ^
Make that initialRamdisk reference conditional on the initrd being enabled.