https://stackoverflow.com/questions/59792850/system-text-json-serialize-null-strings-into-empty-strings-globally

CSharp · Console

/Program.cs

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/59792850/system-text-json-serialize-null-strings-into-empty-strings-globally

    public class EmptyStringConverter : JsonConverter<string>
    {
		public override bool HandleNull => true;
		
        public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
			=> reader.TokenType == JsonTokenType.Null ? "" : reader.GetString();
 
        public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options) =>
            writer.WriteStringValue(value ?? "");
    }
	
    public class Model
    {
        public string FirstName { get; set; }
    }

    class TestClass
    {
        public static void Test()
        {
            var jsonSerializerOptions = new JsonSerializerOptions { Converters = { new EmptyStringConverter() } };
            var json = JsonSerializer.Serialize(new Model() { FirstName = null }, jsonSerializerOptions);
			
			Console.WriteLine(json);

		}
	}

	public class Program
	{
		public static void Main()
		{
			Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());
			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;
			}
		}
		
		public static string GetNetCoreVersion()
		{
			//https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be
			//
			var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;
			var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);
			int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");
			if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)
				return assemblyPath[netCoreAppIndex + 1];
			return "";
		}
	}