Don't ignore nil positional arguments for url helpers - fixes rails#6196

.

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -172,7 +172,7 @@ def #{selector}(*args)
                 options = args.extract_options!
                 result = #{options.inspect}
 
-                if args.any?
+                if args.size > 0
                   result[:_positional_args] = args
                   result[:_positional_keys] = #{route.segment_keys.inspect}
                 end

actionpack/test/dispatch/routing_test.rb

@@ -2571,3 +2571,36 @@ def app; Routes end
     assert_equal "bar", @request.params[:bar]
   end
 end
+
+class TestNamedRouteUrlHelpers < ActionDispatch::IntegrationTest
+  class CategoriesController < ActionController::Base
+    def show
+      render :text => "categories#show"
+    end
+  end
+
+  class ProductsController < ActionController::Base
+    def show
+      render :text => "products#show"
+    end
+  end
+
+  Routes = ActionDispatch::Routing::RouteSet.new.tap do |app|
+    app.draw do
+      scope :module => "test_named_route_url_helpers" do
+        get "/categories/:id" => 'categories#show', :as => :category
+        get "/products/:id" => 'products#show', :as => :product
+      end
+    end
+  end
+
+  def app; Routes end
+
+  include Routes.url_helpers
+
+  test "url helpers do not ignore nil parameters" do
+    get "/categories/1"
+    assert_response :success
+    assert_raises(ActionController::RoutingError) { product_path(nil) }
+  end
+end