Can't override package of home-manager module

[noib3]

Setting a custom package results in the following error:

Error

$ home-manager switch
error:
       … while calling the 'derivationStrict' builtin

         at /builtin/derivation.nix:9:12: (source not available)

       … while evaluating derivation 'home-manager-generation'
         whose name attribute is located at /nix/store/iqxdbcjlg9wx8gdc8bdhy9nsd5imcbjp-source/pkgs/stdenv/generic/make-derivation.nix:334:7

       … while evaluating attribute 'buildCommand' of derivation 'home-manager-generation'

         at /nix/store/iqxdbcjlg9wx8gdc8bdhy9nsd5imcbjp-source/pkgs/build-support/trivial-builders/default.nix:68:16:

           67|         enableParallelBuilding = true;
           68|         inherit buildCommand name;
             |                ^
           69|         passAsFile = [ "buildCommand" ]

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: attribute 'override' missing

       at /nix/store/4wkq348fml5949q5gbyz4fh7y438qzx7-source/nix/hm-module.nix:62:13:

           61|       path = "/share/com.github.Aylur.ags/types";
           62|       pkg = cfg.package.override {
             |             ^
           63|         extraPackages = cfg.extraPackages;

This is a repro from my dotfiles.