DropDownList in the MVC 5 project

I try to modify a view that I create using the controller model generated by the controller, as well as the attached view model, such as view and controller.

In the model, create the parameters as follows:

public class ContactModel
{
[Key]
[DisplayName(“ContactId”)]

public int IDContact {get; together; }
[Required]
[DisplayName(“Tipo de Documento”)]

public int IDType {get; together; }
[DisplayName(“Nombres”)]
public string Name {get; together; }

            public list IDTypeCollection {get; together; }
}

}

Where IdtypeCollection is a list with call to another parametric table or template called paramdocumenttype

The controller and the view are generated by the most viewed mvc 5 driver in the view, the objects remain as follows:

@ Html.LabelFor (model => model.IDType, htmlAttributes: new {@class = "control-label col-md-2"})

@ Html.EditorFor (model => model.IDType, new {htmlAttributes = new {@class = "form-control"}})
@ Html.ValidationMessageFor (model => model.IDType, "", new {@class = "text-danger"})

Where the line is changed

@ Html.EditorFor (model => model.IDType, new {htmlAttributes = new {@class = "form-control"}})

By

@ Html.DropDownListFor (model => model.IDType, new SelectList (Model.IDTypeCollection, "IdType", "NameType"), "Select")

But when you run the application, the following error is generated:

Object reference not established as the object instance.