List <object>を受け入れるメソッドに、リスト<Customer>をパラメータとして渡すことができないのはなぜですか？

Question

次のコードは、私は、このエラーを与える：

Cannot convert from 'System.Collections.Generic.List' to 'System.Collections.Generic.List'.

にはどうすればお客様が実際にオブジェクトを継承するコンパイラに指示することができますか？または、汎用コレクションオブジェクトで継承を行っていないだけです（List<string>を送信すると同じエラーが発生します）。

using System.Collections.Generic; 
using System.Windows; 
using System.Windows.Documents; 

namespace TestControl3423 
{ 
    public partial class Window2 : Window 
    { 
     public Window2() 
     { 
      InitializeComponent(); 

      List<Customer> customers = Customer.GetCustomers(); 
      FillSmartGrid(customers); 

      //List<CorporateCustomer> corporateCustomers = CorporateCustomer.GetCorporateCustomers(); 
      //FillSmartGrid(corporateCustomers); 
     } 


     public void FillSmartGrid(List<object> items) 
     { 
      //do reflection on items and display dynamically 
     } 
    } 

    public class Customer 
    { 
     public string FirstName { get; set; } 
     public string LastName { get; set; } 
     public string Street { get; set; } 
     public string Location { get; set; } 
     public string ZipCode { get; set; } 

     public static List<Customer> GetCustomers() 
     { 
      List<Customer> customers = new List<Customer>(); 
      customers.Add(new Customer { FirstName = "Jim", LastName = "Jones", ZipCode = "23434" }); 
      customers.Add(new Customer { FirstName = "Joe", LastName = "Adams", ZipCode = "12312" }); 
      customers.Add(new Customer { FirstName = "Jake", LastName = "Johnson", ZipCode = "23111" }); 
      customers.Add(new Customer { FirstName = "Angie", LastName = "Reckar", ZipCode = "54343" }); 
      customers.Add(new Customer { FirstName = "Jean", LastName = "Anderson", ZipCode = "16623" }); 
      return customers; 
     } 
    } 
}