nothing is passed to `rack_app` anymore, so rm the params

actionpack/lib/action_dispatch/routing/inspector.rb

@@ -12,7 +12,7 @@ def constraints
         requirements.except(:controller, :action)
       end
 
-      def rack_app(app = self.app)
+      def rack_app
         @rack_app ||= begin
           endpoint = app.app