using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        foreach (var order in Orders) {

            Console.WriteLine(CombinePersonalisationWithCommas(order));

        }

    }

    public static string CombinePersonalisationWithCommas(Order order)

    {

        var result = "";

​

        var personalisations = new List<string>

        {

            order.Personalise1,

            order.Personalise2,

            order.Personalise3,

            order.Personalise4

        };

​

        foreach(var personalisation in personalisations)

        {

            if (!string.IsNullOrWhiteSpace(personalisation))

            {

                result += $"{personalisation}, ";

            }

        }

​

        if (result.Length > 2)

        {

            result = result.Substring(0, result.Length - 2);

        }

​

        return result;

    }

    public static List<Order> Orders = new List<Order> {

        new Order {

            Personalise1 = "aaa",

            Personalise2 = "bbb",

            Personalise3 = "ccc",

            Personalise4 = "ddd"

        },

        new Order {

            Personalise1 = "aaa",

            Personalise2 = "",

            Personalise3 = "ccc",

            Personalise4 = "ddd"

        },

        new Order {

            Personalise1 = "aaa",

            Personalise3 = "ccc",

            Personalise4 = ""

        },

        new Order()

    };

}

​

public class Order {

    public string Personalise1 {get; set;}

    public string Personalise2 {get; set;}

    public string Personalise3 {get; set;}

    public string Personalise4 {get; set;}

}