error when customizing the route in nop 2.7

Hello,

I want to customize routes for my products. So I modify a route in

routes.MapLocalizedRoute("Product",
                                     "my-keyword/{SeName}",
                                     new { controller = "Catalog", action = "Product" },
                                     new[] { "Nop.Web.Controllers" });

Error:

The parameters dictionary contains a null entry for parameter 'productId' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Product(Int32)' in 'Nop.Web.Controllers.CatalogController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
Parameter name: parameters

the original route:

routes.MapLocalizedRoute("Product",
                                     "{SeName}",
                                     new {controller = "Catalog", action = "Product"},
                                     new[] {"Nop.Web.Controllers"});

I don't know why this route can pass the Product ID to the action Product. And I don't how to fix the error above. Could anyone help me?