using System;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public class Test

    {

        public string Test1 {get; set;}

        public string? Test2 {get; set;}

        public bool Test3 {get; set;}

        public bool? Test4 {get; set;}

    }

    public static void Main()

    {

        var body = new Test(){Test1 = "hi"};

        var jsonString = JsonSerializer.Serialize(body, new JsonSerializerOptions { DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault });

        Console.WriteLine("With WhenWritingDefault");

        Console.WriteLine(jsonString);

        jsonString = JsonSerializer.Serialize(body, new JsonSerializerOptions { DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull });

        Console.WriteLine("\n\nWith WhenWritingNull");

        Console.WriteLine(jsonString);

    }

}