using System;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var test = new TestClass();

​

        var jsonWithoutOptions = JsonSerializer.Serialize(test);

        var jsonWithOptions = JsonSerializer.Serialize(test, new JsonSerializerOptions

        {

            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,

        });

        Console.WriteLine(jsonWithoutOptions);

        Console.WriteLine(jsonWithOptions);

        var testRecord = new TestRecord(null);

        var recordWithoutOptions = JsonSerializer.Serialize(testRecord);

        var recordWithOptions = JsonSerializer.Serialize(testRecord, new JsonSerializerOptions

        {

            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,

        });

        Console.WriteLine(recordWithoutOptions);

        Console.WriteLine(recordWithOptions);

    }

}

​

public class TestClass 

{

    public string Test {get; set;}

}

​

public record TestRecord(string Test);