using System;

using System.Collections.Generic;

using System.Linq;

​

public class NullAtLeast : IComparer<int?>

{

    public int Compare( int? left, int? right )

    {

        if ( left == null && right == null )

            return 0;

        if ( left == null )

            return -1;

        if ( right == null )

            return 1;

        return ((int)left).CompareTo((int)right);

    }

}

public class Program

{

    public static void Main()

    {

        var items = new List<int?>{ 1, 2, null, 5, 8, null };

        var ordered = items.OrderBy(i => i, new NullAtLeast()).ToList();

        Console.WriteLine(ordered.Select(i=> i == null ? "null" : i.Value.ToString()).Aggregate((s,f) => s + ", " + f));

    }

}