Correctly use mkMerge

modules/zerotier/default.nix

@@ -1,14 +1,17 @@
 { config, lib, ... }:
-lib.mkMerge [
+{
+  config = lib.mkMerge [
     {
       services.zerotierone = {
         enable = true;
         joinNetworks = [ "632ea29085af0cb4" ];
       };
+
     }
-  (lib.optionalAttrs (config.networking.hostName == "sisko") {
+    (lib.mkIf (config.networking.hostName == "sisko") {
       environment.persistence."/persist".directories = [
         "/var/lib/zerotier-one"
       ];
     })
-]
+  ];
+}