object Reference Not set to and Intense of an Object in mv5

Question

I am using repository pattern in mvc 5 I have created the ICountry Interface and clsCountry class when run the project and put a break point then _ICountry.listofCountry() throw the error "Object reference not send to an Instance". Any expert can tell me where i am wrong . I am using Database first approch and my db extension is .edmx

Model Countries

public int CountryID { get; set; }
public string CountryName { get; set; }

IcountryRepository

public interface ICountry {
List<Countries> listofCountry();
}

clsCountryRepository

public class clsCountry: ICountry {
 ECommercedbEntities _db;
 public clsCountry(ECommercedbEntities db) {
  _db = db;
 }
 public List < Countries > listofCountry() {
  return _db.Countries.ToList();
 }
}

Controller

public class AccountController: Controller {
 ICountry _ICountry;
 public AccountController(ICountry ICountry) {
   _ICountry = ICountry;
  }
  [HttpGet] public ActionResult Registration() {
   try {
    List < Countries > listCountry = _ICountry.listofCountry();
    ViewBag.CountryList = new SelectList(listCountry, "CountryID", "CountryName");
    return View();
   } catch (Exception ex) {
    throw ex;
   }
  }
}

AppStart

public static class UnityConfig {
 public static void RegisterComponents() {
  var container = new UnityContainer();
  container.RegisterType < ILogin, clsLogin > ();
  container.RegisterType < ICountry, clsCountry > ();
  DependencyResolver.SetResolver(new UnityDependencyResolver(container));
 }
}

Global.asax

protected void Application_Start()
{
    UnityConfig.RegisterComponents();
}