using System.ComponentModel;
using System.Web.Mvc;
namespace CustomerWebsite.Mvc
{
 public sealed class EmptyStringToNullModelBinder : DefaultModelBinder
 {
  protected override void SetProperty(ControllerContext controllerContext,
   ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor, object value)
  {
   if (value == null && propertyDescriptor.PropertyType == typeof(string))
   {
    value = string.Empty;
   }

   base.SetProperty(controllerContext, bindingContext, propertyDescriptor, value);
  }
 }
}

ModelBinders.Binders.DefaultBinder = new EmptyStringToNullModelBinder();