Serialize object to empty object {} instead of null with System.Text.Json

Question

Using:

• .net 8
• System.Text.Json serializer.

Let's say I have a two classes defined like this:

public class SampleClass
{
    public SampleClassDetail? FirstProperty { get; set; }
    public SampleClassDetail? SecondProperty { get; set; }
}

public class SampleClassDetail
{
    public int MyProperty { get; set; }
}

And an instance of SampleClass :

SampleClass sample = new()
{
    FirstProperty = new SampleClassDetail { MyProperty = 1 }
};

Then I want to serialize it with System.Text.Json: string serialized = JsonSerializer.Serialize(sample);

This produces:

{
  "FirstProperty": {
    "MyProperty": 1
  },
  "SecondProperty": null
}

But I would the null to be treated like: "SecondProperty": {}

I've tried creating a CustomJson Converter and adding it to the options:

public class SampleClassDetailConverter : JsonConverter<SampleClassDetail?>
{
    public override SampleClassDetail? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }

    public override void Write(Utf8JsonWriter writer, SampleClassDetail? value, JsonSerializerOptions options)
    {
        if (value == null)
        {
            writer.WriteStartObject();
            writer.WriteEndObject();
        }
        else
        {
            var newOptions = new JsonSerializerOptions(options);
            newOptions.Converters.Remove(this);
            JsonSerializer.Serialize(writer, value, newOptions);
        }
    }
}

var options = new JsonSerializerOptions();
options.Converters.Add(new SampleClassDetailConverter());

string serialized = JsonSerializer.Serialize(sample, options);

But still getting the same.

dotnetfiddle