only output the plugin copy loop if plugins are enabled

modules/minecraft.nix

@@ -2486,9 +2486,11 @@ in
         # Update the plugins
         mkdir -p plugins
         rm -rf plugins/*.jar
+        ${if cfg.plugins == [] then "" else ''
           for f in ${builtins.toString cfg.plugins}; do
             cp $f plugins
           done
+        ''}
       '';
       serviceConfig = {
         Type = "simple";