missing `boot.loader.grub.devices` when using btrfs-subvolumes example

When trying to `sudo nixos-install` it errors saying the `boot.loader.grub.devices` option is missing, even though the quickstart guide says this option shouldn't be filled because disko will do it automatically.

Here is the config: https://github.com/J0pper/nixos
go under `hosts/lenovo-y520` and most modules are imported in the `flake.nix`