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

​

//https://stackoverflow.com/questions/66495660/net-5-0-signature-change-of-system-text-json-jsonserializer-deserialize

​

#nullable enable

​

    public static class ObjectExtensions

    {

        public static T ThrowOnNull<T>(this T? value) where T : class => value ?? throw new ArgumentNullException();

    }

​

    class TestClass

    {

        public static void Test()

        {

            object? obj1 = JsonSerializer.Deserialize<object>("null"); // Does not throw; explicitly typed for clarity.

            Assert.IsNull(obj1);     // Passes

            var array = JsonSerializer.Deserialize<int []>("null");    // Does not throw;

            Assert.IsNull(array);    // Passes

            var nullable = JsonSerializer.Deserialize<int?>("null");   // Does not throw;

            Assert.IsNull(nullable); // Passes

​

            try

            {

                #nullable enable

                object obj2 = JsonSerializer.Deserialize<object>("null"); // Compiler warning: Converting null literal or possible value to non-nullable type;

                var i = JsonSerializer.Deserialize<int>("null");  // Throws, since int is a non-nullable value type.

            }

            catch (JsonException ex)

            {

                Console.WriteLine("Caught expected exception {0}", ex.Message);

            }

            Test1();

            Test2<object>();

        }

        static void Test1()

        {

            object? obj = JsonSerializer.Deserialize<object>("null");

            Console.WriteLine($"obj == null = {obj == null}");

        }

        static void Test2<TValue>() where TValue : class

        {

            try

            {

                var json = "null";

                var value = JsonSerializer.Deserialize<TValue>(json).ThrowOnNull();

            }

            catch (ArgumentNullException ex)

            {

                Console.WriteLine("Caught expected exception {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;

            }

        }

    }

​