using System;

using System.Collections.Generic;   

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var result = new List<string>

            {

                "B",

                string.Empty,

                "A"

            };

        var res = from s in result orderby string.IsNullOrEmpty(s) select s;

        Console.WriteLine(string.Join(",", res));

    }

}