using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(MapContentSourceToString(null));

    }

    public static string MapContentSourceToString(ContentSourceType? contentSourceType)

    {

        string mappedSource = "NoSubscription";

        switch (contentSourceType.GetValueOrDefault())

        {

            case ContentSourceType.ExternalProvider:

                mappedSource = "External";

                break;

            case ContentSourceType.CornerstoneLibrary:

                mappedSource = "CSOD";

                break;

            case ContentSourceType.Both:

                mappedSource = "CSOD";

                break;

            default:

                mappedSource = "NoSubscription";

                break;

        }

​

        return mappedSource;

    }

    public enum ContentSourceType

    {

        ExternalProvider,

        CornerstoneLibrary,

        Both

    }

}