LINQ to Entities and creating a new instance of an entity

context.Customers newCustomer = context.Customers.CreateCustomer(...);
newCustomer.FirstName = firstNameTextBox.Text;
newCustomer.Address.Street = streetTextBox.Text;   // this is where the error is thrown

newCustomer.Address = new Address()
    {
        Street = streetTextBox.Text,
        // etc.
    };

newCustomer.Address = (from Addresses in context where ...).FirstOrDefault();
if (newCustomer.Address == null)
{
    newCustomer.Address = new Address()
        {
            Street = streetTextBox.Text,
            // etc.
        };
}