nixos/h2o: virtual host settings default to empty

Author: toastal

nixos/modules/services/web-servers/h2o/vhost-options.nix

@@ -195,6 +195,7 @@ in
 
     settings = mkOption {
       type = types.attrs;
+      default = { };
       description = ''
         Attrset to be transformed into YAML for host config. Note that the HTTP
         / TLS configurations will override these config values.