Plocate unusable

Help
1

I installed plocate using configuration.nix file:

  environment = {

    systemPackages = with pkgs; [
....
      plocate
    ];
  };

But I have tried to enable the associated systemd units in configuration.nix but it fails:

$ cat configuration.nix
....
  services = {
    plocate.enable = true;
....

$ doas nixos-rebuild switch
error: The option `services.plocate' does not exist. Definition values:
       - In `/etc/nixos/configuration.nix':
           {
             enable = true;
           }
(use '--show-trace' to show detailed location information)
building Nix...
2 
{
  services.locate = {
    enable = true;
    locate = pkgs.plocate;
  };
}
3

I had warnings

trace: warning: The option `services.locate.locate' defined in `/etc/nixos/configuration.nix' has been renamed to `services.locate.package'.
trace: warning: mlocate and plocate do not support the services.locate.localuser option. updatedb will run as root. Silence this warning by setting services.locate.localuser = null.

so I used

  services.locate = {
    enable = true;
    package = pkgs.plocate;
    localuser = null;
  };

No idea what the localuser option exactly means.