public int Compare(Product first, Product second) {            return PartialComparer.RefernceCompare(first, second) ?? PartialComparer.Comare(first.Popularity, second.Popularity) ?? PartialComparer.Comare(first.Price, second.Price) ?? PartialComparer.Comare(first.Name, second.Name) ?? 0;        }    }    public static class PartialComparer {        public static int? Comare<T>(T first, T second) {            return Compare(Comparer<T>.Default, first, second);        }        public static int? Compare<T>(IComparer<T> comparer, T first, T second) {            int ret = comparer.Compare(first, second);            return ret == 0 ? new int?() : ret;        }        public static int? RefernceCompare<T>(T first, T second) where T : class {            return first == second ? 0 : (first == null ? -1 : (second == null ? 1 : new int?()));        }    }