using System;

using System.Text.Json;

public class Program

{

    public static void Main()

    {

        var s = "";

        var s2 = """{ "thing": null }""";

        var result = JsonSerializer.Deserialize<Test>(s);

        var result2 = JsonSerializer.Deserialize<Test>(s2);

        Console.WriteLine(result);

        Console.WriteLine(result2);

    }

    public record Test(Guid? thing);

}