using System;

using System.Text.Json;

using System.Text.Json.Serialization;

​

string jsonStr = """

                { "mainInfo": {} }

                """;

​

JsonSerializerOptions options = new()

{

    WriteIndented = true,

    PropertyNamingPolicy = JsonNamingPolicy.CamelCase

};

​

TypeA result = JsonSerializer.Deserialize<TypeA>(jsonStr, options);

​

Console.WriteLine(JsonSerializer.Serialize(result, options));

​

public class MyClass

{

    public const int MyConstantInt = 42;

    public const string MyConstantString = "Hello, World!";

}

​

​

public class TypeA 

{

    [JsonConverter(typeof(NullableObjectConverter<MainInfo>))]

    public MainInfo? MainInfo { get; set; }

}

​

public class MainInfo

{

    public string? Name { get; set; }

    public string? Address { get; set; }

}

​

public class NullableObjectConverter<T> : JsonConverter<T> where T : class

{

    public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

    {

        if (reader.TokenType == JsonTokenType.StartObject)

        {

            using JsonDocument doc = JsonDocument.ParseValue(ref reader);

            if (doc.RootElement.EnumerateObject().MoveNext()) // Check if there's at least one property

            {

                return JsonSerializer.Deserialize<T>(doc.RootElement.GetRawText(), options);

            }

            return null; // Empty object `{}` is treated as `null`

        }

        return JsonSerializer.Deserialize<T>(ref reader, options);

    }

​

    public override void Write(Utf8JsonWriter writer, T? value, JsonSerializerOptions options)

    {

        JsonSerializer.Serialize(writer, value, options);

    }

}

​