why whenever I fill the form MembershipType value comes as null value?

The parameters dictionary contains a null entry for parameter 'membershipTypeId' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult CustomerForm(Int32, System.String, Boolean, Int32)' in 'WebApplication2.Controllers.CustomerController'.An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

My customer class which has a many - to one relationship with membershipType class:

  public class Customer
    {
        public Customer()
        {
            this.Movies = new HashSet<Movie>();
        }
        public int id { get; set; }
        [Required]
        [StringLength(255)]
        public String Name { get; set; }
        public bool IsSubscribedToNewsletter { get; set; }
        public int CurrentMembershipTypeId { get; set; }
        public MembershipType CurrentMembershipType { get; set;}
        public ICollection<Movie> Movies { get; set; }
    }

My MembershipType class:

 public class MembershipType
    {
        public int Id { get; set; }
        public short SignupFee { get; set; }
        public byte DurationInMonths { get; set; }
        public byte DiscountRate { get; set; }
        public ICollection<Customer> Customers { get; set; }

        // public virtual ICollection<Movie> Movie { get; set; }
    }

My CustoemrController: get Function for customer form:

 public ActionResult CustomerForm(Customer customer)
        {
            var membershipTypes = iMembershipTypeRepository.GetMembershipTypes();
            ViewBag.Message = "Customers form is going to display: ";
            if (customer.IsSubscribedToNewsletter != true)
                ViewBag.Addon = "Selected";
            else
                ViewBag.Addon = "Not Selected";
            return View(membershipTypes);
        }

Post action for Customer form:

[HttpPost]    
        public ActionResult CustomerForm(int CustomerId, string CustomerName, bool CustomerisSubscribedToNewsLetter, int membershipTypeId)

            {

                Customer customer = new Customer();

                customer.id = CustomerId;

                customer.Name = CustomerName;

                customer.IsSubscribedToNewsletter = CustomerisSubscribedToNewsLetter;
                customer.CurrentMembershipTypeId = membershipTypeId;

                iCustomerRepository.InsertCustomer(customer);

                iCustomerRepository.Save();

                return RedirectToAction("Customer");

            }

CustomerForm view:

<h2>CustomerForm</h2>

<form action="/Customer/CustomerForm" method="post">
    <table>
        <tr>
            <td>Id:</td>
            <td><input id="CustomerId" type="text" name="CustomerId" /></td>
        </tr>
        <tr>
            <td>Name:</td>
            <td><input id="CustomerName" type="text" name="CustomerName" /></td>
        </tr>
        <tr>
            <td>IsSubscribedToNewLetter:</td>
            <td><input id="CustomerisSubscribedToNewsLetter" type="text" name="CustomerisSubscribedToNewsLetter" /></td>
        </tr>
        <tr>
            <td>MembershipType:</td>
            <td>
                <select id="MembershipTypeId" name="MembershipTypes">
                    @foreach (var membershipType in @Model)
                    {
                        <option value=@membershipType.Id>
                            @*@membershipType.SignupFee*@
                            @membershipType.Id
                        </option>
                    }
                </select>
            </td>
        </tr>

    </table>
    <input type="submit" value="save"/>
</form>