Mantenha as linhas NULL por último no Dynamic Linq Order By

Estou usando este snippet abaixo para solicitar dinamicamente minhas consultas Linq e funciona muito bem. Eu não sou bom em reflexão ou consultas linq complexas, mas preciso de uma maneira que, quando a ordem crescente for usada, os valores NULL sejam os últimos e vice-versa.

Portanto, se o nome da minha propriedade fosse um número inteiro e os valores da coluna fossem 1, 3, 5, todas as linhas NULL estariam no final, não no início por padrão. O que posso adicionar a esta expressão para que isso aconteça?

Esse código funciona com a estrutura da entidade e ainda é necessário para a comparação NULL.

Exemplo

list.OrderBy("NAME DESC").ToList()

Classe

   public static class OrderByHelper
    {
        public static IOrderedQueryable<T> ThenBy<T>(this IEnumerable<T> enumerable, string orderBy)
        {
            return enumerable.AsQueryable().ThenBy(orderBy);
        }

        public static IOrderedQueryable<T> ThenBy<T>(this IQueryable<T> collection, string orderBy)
        {
            if (string.IsNullOrWhiteSpace(orderBy))
                orderBy = "ID DESC";

            IOrderedQueryable<T> orderedQueryable = null;

            foreach (OrderByInfo orderByInfo in ParseOrderBy(orderBy, false))
                orderedQueryable = ApplyOrderBy<T>(collection, orderByInfo);

            return orderedQueryable;
        }

        public static IOrderedQueryable<T> OrderBy<T>(this IEnumerable<T> enumerable, string orderBy)
        {
            return enumerable.AsQueryable().OrderBy(orderBy);
        }

        public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> collection, string orderBy)
        {
            if (string.IsNullOrWhiteSpace(orderBy))
                orderBy = "ID DESC";

            IOrderedQueryable<T> orderedQueryable = null;

            foreach (OrderByInfo orderByInfo in ParseOrderBy(orderBy, true))
                orderedQueryable = ApplyOrderBy<T>(collection, orderByInfo);

            return orderedQueryable;
        }

        private static IOrderedQueryable<T> ApplyOrderBy<T>(IQueryable<T> collection, OrderByInfo orderByInfo)
        {
            string[] props = orderByInfo.PropertyName.Split('.');
            Type type = typeof(T);

            ParameterExpression arg = Expression.Parameter(type, "x");
            Expression expr = arg;
            foreach (string prop in props)
            {
                // use reflection (not ComponentModel) to mirror LINQ
                PropertyInfo pi = type.GetProperty(prop, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
                expr = Expression.Property(expr, pi);
                type = pi.PropertyType;
            }
            Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
            LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
            string methodName = String.Empty;



            if (!orderByInfo.Initial && collection is IOrderedQueryable<T>)
            {
                if (orderByInfo.Direction == SortDirection.Ascending)
                    methodName = "ThenBy";
                else
                    methodName = "ThenByDescending";
            }
            else
            {
                if (orderByInfo.Direction == SortDirection.Ascending)
                    methodName = "OrderBy";
                else
                    methodName = "OrderByDescending";
            }

            return (IOrderedQueryable<T>)typeof(Queryable).GetMethods().Single(
                method => method.Name == methodName
                        && method.IsGenericMethodDefinition
                        && method.GetGenericArguments().Length == 2
                        && method.GetParameters().Length == 2)
                .MakeGenericMethod(typeof(T), type)
                .Invoke(null, new object[] { collection, lambda });
        }

        private static IEnumerable<OrderByInfo> ParseOrderBy(string orderBy, bool initial)
        {
            if (String.IsNullOrEmpty(orderBy))
                yield break;

            string[] items = orderBy.Split(',');

            foreach (string item in items)
            {
                string[] pair = item.Trim().Split(' ');

                if (pair.Length > 2)
                    throw new ArgumentException(String.Format("Invalid OrderBy string '{0}'. Order By Format: Property, Property2 ASC, Property2 DESC", item));

                string prop = pair[0].Trim();

                if (String.IsNullOrEmpty(prop))
                    throw new ArgumentException("Invalid Property. Order By Format: Property, Property2 ASC, Property2 DESC");

                SortDirection dir = SortDirection.Ascending;

                if (pair.Length == 2)
                    dir = ("desc".Equals(pair[1].Trim(), StringComparison.OrdinalIgnoreCase) ? SortDirection.Descending : SortDirection.Ascending);

                yield return new OrderByInfo() { PropertyName = prop, Direction = dir, Initial = initial };

                initial = false;
            }

        }

        private class OrderByInfo
        {
            public string PropertyName { get; set; }
            public SortDirection Direction { get; set; }
            public bool Initial { get; set; }
        }

        private enum SortDirection
        {
            Ascending = 0,
            Descending = 1
        }