anchor.diff:        };
         ipAddress = mkOption {
           default = null;
  +        type = types.nullOr types.str;
           description = ''
             IP address to assign to GVPE interface
           '';
         };
         subnet = mkOption {
           default = null;
  +        type = types.nullOr types.str;
           example = "10.0.0.0/8";
           description = ''
             IP subnet assigned to GVPE network
  
positive.code: 
        nodename = mkOption {
          default = null;
          description =''
            GVPE node name
          '';
        };
        configText = mkOption {
          default = null;
          example = ''
            tcp-port = 655
            udp-port = 655
  
negative.code: {config, pkgs, lib, ...}:
  
  let
    inherit (lib) mkOption mkIf types;
  
    cfg = config.services.gvpe;
  
  