using System;

using System.Collections.Generic;

using System.Linq;              

public class Program

{

    public static void Main()

    {

        string fname = "a";

        string lname = "";

        List<string> names = new List<string>{fname.Trim(), lname.Trim()};

        string fullname = String.Join(",", names.Where(s=>!string.IsNullOrWhiteSpace(s)).ToList());

        Console.WriteLine(fullname);

    }

}