Assert modules before importing into the config?

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I am writing some custom functions for extracting the user config (users.users.<name>) from other configurations, as I want to make the config stateless and easy to share.

  mkSystem = mkExtendable ({ system, inputs, modules ? { } }:
    let
      hasHm = (builtins.hasAttr "home-manager" inputs)
        || (builtins.hasAttr "hm" inputs);

      injected = (builtins.map (m:
        let
          # Import and do the assertion for the input
          imported = if builtins.isPath m then (import m) inputs.nixpkgs else m;
          checked = imported;
        in (checked)) (toList modules));

    in (inputs.nixpkgs.lib.nixosSystem {
      inherit system;
      modules = (checked) ++ (inputs.nixpkgs.lib.optional hasHm
        inputs.home-manager.nixosModules.home-manager);
      specialArgs = { inherit inputs system; };
    }));

I think the most ideomatic way for assertion in nixos would be doing with the assertions like this, a random piece of code from HM:

But I cannot assert it like this, because by default the users.users.<name> will have root and nobody, and I don’t want to mess with them.

And the import I have right now, gives me this error:

error: anonymous function at /nix/store/739czqh6li2gbg88llj08lkjsn16dhfw-source/hardware-configuration.nix:4:1 called without required argument 'config'

       at /nix/store/la7x9ljhi2lllh8cf1hcnl80nrz1s439-source/lib.nix:73:48:

           72|         let
           73|           imported = if builtins.isPath m then (import m) inputs.nixpkgs else m;
             |                                                ^
           74|           checked = imported;
(use '--show-trace' to show detailed location information)

Can I import the modules here with import? How can I do that?