using System;

public class Program

{

    public static void Main()

    {

        var rule = new BillingGroupRule();

        Console.WriteLine(rule.Id); // Non-nullable guid default = empty guid

        Console.WriteLine(rule.BillingGroupId.GetValueOrDefault()); // Nullable guid call to GetValueOrDefault 

        Console.WriteLine(rule.BillingGroupId == null ? "null" : rule.BillingGroupId.ToString());

        Console.WriteLine("The value: '" + rule.BillingGroupId + "'"); // Nullable guid default = null

        Guid? gooid = rule.BillingGroupId.GetValueOrDefault();

        Console.WriteLine(gooid);

        Guid? gooid2 = rule.BillingGroupId;

        Console.WriteLine(gooid2);

        Console.WriteLine(rule.LossDateStart == null);

        Console.WriteLine(rule.LossDateStart.GetValueOrDefault());

        Console.WriteLine(rule.LossDateStart.GetValueOrDefault().Date);

        rule.LossDateStart = null;

        Console.WriteLine(rule.LossDateStart == null);

        Console.WriteLine(rule.LossDateStart.GetValueOrDefault());

        Console.WriteLine(rule.LossDateStart.GetValueOrDefault().Date);

    }

    internal class BillingGroupRule {

        public Guid Id { get; set; }

​

        public Guid? BillingGroupId { get; set; }

​

        public string Datasets { get; set; }

​

        public string CatCodes { get; set; }

​

        public string States { get; set; }

​

        public DateTime? LossDateStart { get; set; }

​

        public DateTime? LossDateEnd { get; set; }

​

        public string DateType { get; set; }

​

        public string LossTypes { get; set; }

​

        public int? ProcessingOrder { get; set; }

    }

}