Error in GetCount () does not come out of the infinite loop.

Apr 19 at 6:24 PM
"An unhandled exception of type 'System.StackOverflowException' occurred in mscorlib.dll"


public int GetCount()
    {
        // Get the count of each item in the cart and sum them up
        int? count = (from cartItems in storeDB.Carts
                      where cartItems.CartId == ShoppingCartId
                      select (int?)cartItems.Count).Sum();
        // Return 0 if all entries are null
        return count ?? 0;

    }