allow URL helpers to work with optional scopes

actionpack/CHANGELOG.md

+*   Fixed usage of optional scopes in URL helpers.
+
+    *Alex Robbin*
+
 *   Fixed handling of positional url helper arguments when `format: false`. 
 
     Fixes #17819.

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -293,7 +293,7 @@ def handle_positional_args(controller_options, inner_options, args, result, path
                 path_params -= result.keys
               end
               path_params.each { |param|
-                result[param] = inner_options[param] || args.shift
+                result[param] = inner_options.fetch(param) { args.shift }
               }
             end
 

actionpack/test/dispatch/routing/route_set_test.rb

@@ -160,6 +160,18 @@ def call(env)
         assert_equal '/foo/1/bar/2', url_helpers.foo_bar_path(2, foo_id: 1)
       end
 
+      test "having an optional scope with resources" do
+        draw do
+          scope "(/:foo)" do
+            resources :users
+          end
+        end
+
+        assert_equal '/users/1', url_helpers.user_path(1)
+        assert_equal '/users/1', url_helpers.user_path(1, foo: nil)
+        assert_equal '/a/users/1', url_helpers.user_path(1, foo: 'a')
+      end
+
       test "stringified controller and action keys are properly symbolized" do
         draw do
           root 'foo#bar'