urbackup2-server: dataset options are not optional

[xieve]

Hey there, first of all: thank you for making this stuff accessible. Have you thought about contributing some of your packages to the official repos?

Issue

Since the dataset options are meant to be optional, I am assuming you were meaning to implement this config as optional by defaulting to null.

However, if I don't specify service.urbackup.dataset.images and service.urbackup.dataset.files, the activation of my config fails with one of these two error messages:

error: The option `environment.etc."urbackup/dataset".source' is used but not defined.

error: The option `environment.etc."urbackup/dataset_file".source' is used but not defined.

Workaround

Specifying an empty string for both attributes makes the error go away, without specifying any config I do not actually want.

Background

I am trying to set up your urbackup server module, which currently looks like this:

# flake.nix
{
    description = "xieve's nixos flake";

    inputs = {
        nixpkgs = {
            url = "github:NixOS/nixpkgs/nixos-unstable";
        };
        nzbr = {
            url = "github:nzbr/nixos";
        };
    };

    outputs = { self, nixpkgs, nzbr }@attrs: {
        nixosConfigurations = {
            thegreatbelow = nixpkgs.lib.nixosSystem {
                system = "x86_64-linux";
                specialArgs = attrs; # Pass inputs to modules
                modules = [
                    nzbr.nixosModules."service/urbackup.nix"
                    ./thegreatbelow.nix
                ];
            };
        };
    };
}

# thegreatbelow.nix
{ config, pkgs, nzbr, ... }:

{
    # [...]
    nzbr.service.urbackup = {
        enable = true;
        backupfolder = "/mnt/user/urbackup/";
        config = {
            LOGFILE = "/mnt/user/appdata/binhex-urbackup/urbackup/log/urbackup.log";
        };
        package = nzbr.packages.x86_64-linux.urbackup2-server;
        dataset.images = ""; # WORKAROUND HERE
        dataset.files = ""; # WORKAROUND HERE
    };
    fileSystems."/var/urbackup" = {
        device = "/mnt/user/appdata/binhex-urbackup/urbackup";
        fsType = "none";
        options = [ "bind" ];
    };
    # [...]
}

I am moving away from a docker-based setup, but before I move all my files, I want to get this thing running as a proof of concept. These backups are not extremely critical, I am comfortable with "fuck around, find out".

I do not have a proposed solution for this, because I am not too sure myself what the best way to resolve this would be. I am very new to Nix.