fix(nixos): support Gitea without a reverse proxy

configs/nixos/modules/services/gitea.nix

@@ -11,7 +11,8 @@ in
     enable = lib.mkEnableOption "Gitea";
 
     reverseProxyAddress = lib.mkOption {
-      type = lib.types.str;
+      type = lib.types.nullOr lib.types.str;
+      default = null;
       description = "IP address of the reverse proxy trusted to forward client headers.";
     };
   };
@@ -55,6 +56,8 @@ in
             START_SSH_SERVER = true;
             SSH_LISTEN_HOST = "0.0.0.0";
             SSH_LISTEN_PORT = 2222;
+          }
+          // lib.optionalAttrs (cfg.reverseProxyAddress != null) {
             REVERSE_PROXY_TRUSTED_PROXIES = "${cfg.reverseProxyAddress}/32";
           };
           service.DISABLE_REGISTRATION = true;