using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

​

using System.Text.Json;

using System.Text.Json.Serialization;

using System.Text.Json.Serialization.Metadata;

using System.Text.Json.Nodes;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/77072548/how-to-deserialize-array-with-null-values

​

#nullable enable

​

    public class JsonNodeListConverter : JsonConverter<IEnumerable<JsonNode?>>

    {

        public override bool CanConvert(Type objectType) => 

            objectType == typeof(List<JsonNode>) || objectType == typeof(IReadOnlyList<JsonNode>) || objectType == typeof(IReadOnlyCollection<JsonNode>) || objectType == typeof(JsonNode [])  || objectType == typeof(IEnumerable<JsonNode>);

        public override void Write(Utf8JsonWriter writer, IEnumerable<JsonNode?> value, JsonSerializerOptions options)

        {

            writer.WriteStartArray();

            foreach (var node in value)

                JsonSerializer.Serialize(writer, node, options);

            writer.WriteEndArray();

        }

        public override IEnumerable<JsonNode?> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) 

        {

            if (reader.TokenType != JsonTokenType.StartArray)

                throw new JsonException();

            var list = new List<JsonNode?>();

            while (reader.ReadAndAssert().TokenType != JsonTokenType.EndArray)

            {

                list.Add(JsonSerializer.Deserialize<JsonNode>(ref reader, options));

            }

            return typeToConvert.IsArray ? list.ToArray() : list;

        }

    }

​

    public static class JsonExtensions

    {

        public static ref Utf8JsonReader ReadAndAssert(ref this Utf8JsonReader reader) { if (!reader.Read()) { throw new JsonException(); } return ref reader; }

    }

​

​

    public record Obj(JsonNode value);

​

    class TestClass

    {

        public static void Test()

        {

            var options = new JsonSerializerOptions

            {

                Converters = { new JsonNodeListConverter() },

            };

​

            Test("""{"value":null}""", () =>

                JsonSerializer.Deserialize<JsonNode>("null", options)

            );

            Test("""{"value":null}""", () =>

                JsonSerializer.Deserialize<Obj>("""{"value":null}""", options)

            );

            Test("""[1]""", () =>

                JsonSerializer.Deserialize<List<JsonNode>>("""[1]""", options)

            );

            Test("""["a"]""", () =>

                JsonSerializer.Deserialize<List<JsonNode>>("""["a"]""", options)

            );

​

            Test("""[null]""", () =>

                JsonSerializer.Deserialize<List<JsonNode>>("""[null]""", options)

            );

            Test("""[null]""", () =>

                JsonSerializer.Deserialize<List<JsonNode?>>("""[null]""", options)

            );

            Test("""[null]""", () =>

                JsonSerializer.Deserialize<IReadOnlyList<JsonNode>>("""[null]""", options)

            );

            Test("""[null]""", () =>

                JsonSerializer.Deserialize<JsonNode []>("""[null]""", options)

            );

            Test("""[null]""", () =>

                JsonSerializer.Deserialize<JsonNode? []>("""[null]""", options)

            );

            Test("""[null]""", () =>

                JsonSerializer.Deserialize<IEnumerable<JsonNode>>("""[null]""", options)

            );

            Test("""[null, [null], 1, {}, "a"]""", () =>

                 {

                     var list = JsonSerializer.Deserialize<List<JsonNode?>>("""[null, [null], 1, {}, "a"]""", 

                                                                                options);

                     return list;

                 }

            );

        }   

​

        static void Test<T>(string json, Func<T> test)

        {

            var options = new JsonSerializerOptions

            {

                Converters = { new JsonNodeListConverter() },

            };

            try

            {

                Console.WriteLine("Testing deserialization of {0} to {1}:", json, typeof(T));

                var value = test();

                Console.WriteLine("   Result: {0}", JsonSerializer.Serialize(value, options));

            }

            catch (Exception ex)

            {

                Console.WriteLine("   FAILED with exception:\n   {0}", ex.Message);

            }

        }

    }

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine("System.Text.Json version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​