Object reference not set to an instance of an object

Question

Controller

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(ContactDetailViewModel model)
{
if (ModelState.IsValid)
{
model.Id = _Login.GetCurrentUserCustomer().Id;
using (var dbContextScope = _dbContextScopeFactory.Create())
{
Contact contact = model;
contact.ContactAttributes = new List<ContactAttribute>();
var user = _Login.GetCurrentUser();
if(model.Attributes != null)
{
foreach (var item in model.Attributes)
{
if (item.AddressValue != null)
{
ContactAttribute attribute = new ContactAttribute()
{
AttributeValue = item.AddressValue,
Code = item.AddressElement,
Contact = contact//,
};
_ContactRepo.UpdateContactAttribute(attribute, user);
contact.ContactAttributes.Add(attribute);
}
}
}
try
{
_ContactRepo.UpdateContact(contact, user);
}
catch (RMException rme)
{
rme.Log();
ModelState.AddModelError("", "Updating contact failed. Please check your values and try again.");
return PartialView(model);
}
dbContextScope.SaveChanges();
}
}
else
{
return PartialView(model);
}
return RedirectToAction("Index", "Contact");
}

Model

public ContactAttribute UpdateContactAttribute(ContactAttribute attribute, User user)
{
var dbAttribute = DbContext.ContactAttributes.Find(attribute.ContactId);
dbAttribute.AttributeValue = attribute.AttributeValue;
dbAttribute.Code = attribute.Code;
UpdateWithUser(dbAttribute, user.UserId, "ContactRepo.UpdateContactAttribute");
return dbAttribute;
}