如何将ASP.NET MVC所有参数均自动设置为默认

public class HomeController : Controller
{
    public ActionResult Index(int para1,string para2,int para3,bool para4)
    {
        return View();
    }
}

<span><h1>“/”应用程序中的服务器错误。<hr color="silver" size="1" width="100%"></h1>
<h2> <i>对于“MvcApplication1.Controllers.HomeController”中方法“System.Web.Mvc.ActionResult Index(Int32, System.String, Int32, Boolean)”的不可以为 null 的类型“System.Int32”的参数“para1”，参数字典包含一个 null 项。可选参数必须为引用类型、可以为 null 的类型或声明为可选参数。<br>参数名: parameters</i> </h2></span>

public class HomeController : Controller
    {
        protected override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var methodInfo = ((ReflectedActionDescriptor) filterContext.ActionDescriptor).MethodInfo;
            foreach (var p in methodInfo.GetParameters())
            {
                if (p.ParameterType.IsValueType)
                {
                    filterContext.ActionParameters[p.Name] = Activator.CreateInstance(p.ParameterType);
                }
            }
        }

        public ActionResult Index(int para1, string para2, int para3, bool para4)
        {
            Debug.Print("para1:{0} para2:{1} para3:{2} para4 :{3}",para1, para2,  para3, para4);
            return View();
        }
    }