using System;

using System.Xml.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Build(true));

        Console.WriteLine(Build(false));

    }

    private static XElement Build(bool includeDetails) => new XElement("Test",

        new XElement("Foo", 42),

        includeDetails ? new XElement("Bar", Guid.NewGuid()) : null,

        includeDetails ? new XElement("Baz", DateTime.Now) : null

    );

}