Avoid nulls in C# Class

Question

Hi,

I have the following class which gets the data from MySQL database.

class SigninData
{
    public string user_id { get; set; }
    public string user_uuid { get; set; }
    public string first_name { get; set; }
    public string last_name { get; set; }
    public string email_address { get; set; }
    public string country { get; set; }
}

But in some cases, the country will return null then my code will crash with the following error:

System.ArgumentNullException has been thrown

on this line:

List<SigninData> data = System.Text.Json.JsonSerializer.Deserialize<List<SigninData>>(result);

How can I avoid this?

Thanks,
Jassim

Answer 1

See Microsoft Learn Ignore individual properties which shows several variants code samples also.

Edit

See if this works for you

using System;  
using System.Collections.Generic;  
using System.IO;  
using System.Text.Json;  
using System.Text.Json.Serialization;  
  
namespace DeserializeAvoidNullConsoleApp  
{  
    class Program  
    {  
        private static string _fileName = "data.json";  
        static void Main(string[] args)  
        {  
            Write();  
  
            var list = Read();  
  
            foreach (var data in list)  
            {  
                Console.WriteLine($"{data.first_name, -10}{data.country, -10} {(data.country is null)}");  
            }  
  
            Console.ReadLine();  
        }  
  
        private static List<SigninData> Read()   
            => JsonSerializer.Deserialize<List<SigninData>>(File.ReadAllText(_fileName));  
  
        private static void Write()  
        {  
            List<SigninData> signinData = new()  
            {  
                new () { country = null, first_name = "Bob", last_name = "Smith", email_address = "bob@gmail", user_id = "A1", user_uuid = "Whatever" },  
                new () { country = "Germany", first_name = "Anne", last_name = "Smith", email_address = "A@gmail", user_id = "B1", user_uuid = "XXXX" }  
            };  
  
            var options = JsonSerializerOptions();  
              
            File.WriteAllText(_fileName, JsonSerializer.Serialize(signinData, options));  
  
        }  
  
        private static JsonSerializerOptions JsonSerializerOptions() =>  
            new ()  
            {  
                WriteIndented = true,  
                Converters = { new NullToEmptyStringConverter() }  
            };  
    }  
  
    class SigninData  
    {  
        public string user_id { get; set; }  
        public string user_uuid { get; set; }  
        public string first_name { get; set; }  
        public string last_name { get; set; }  
        public string email_address { get; set; }  
        public string country { get; set; }  
    }  
  
    public class NullToEmptyStringConverter : JsonConverter<string>  
    {  
        public override bool HandleNull => true;  
        public override bool CanConvert(Type typeToConvert)   
            => typeToConvert == typeof(string);  
        public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)   
            => throw new NotImplementedException();  
        public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options)  
        {  
            writer.WriteStringValue(value ?? "");  
        }  
    }  
}  

Json

[  
  {  
    "user_id": "A1",  
    "user_uuid": "Whatever",  
    "first_name": "Bob",  
    "last_name": "Smith",  
    "email_address": "bob@gmail",  
    "country": ""  
  },  
  {  
    "user_id": "B1",  
    "user_uuid": "XXXX",  
    "first_name": "Anne",  
    "last_name": "Smith",  
    "email_address": "A@gmail",  
    "country": "Germany"  
  }  
]  

Answer 2

A null or empty country value should no cause an error with the JsonSerializer. I suspect there are other issues with your code that you have not share with the community. For example trying to access country members without checking if the variable is null.

item.country?.Trim()  

[Null-conditional operators ?. and ?
?? and ??= operators (C# reference)

Example code

static void Main(string[] args)  
{  
    List<SigninData> mockQueryResults = new List<SigninData>()  
    {  
        new SigninData() {  
            email_address = "hello@world.com",  
            first_name = "hello",  
            last_name = "world",  
            user_id = "1",  
            user_uuid ="11",  
            country = null  
        },  
        new SigninData() {  
            email_address = "foo@bar.com",  
            first_name = "foo",  
            last_name = "bar",  
            user_id = "2",  
            user_uuid ="22",  
            country = "USA"  
        }  
    };  
  
    string result = JsonSerializer.Serialize<List<SigninData>>(mockQueryResults);  
    Console.WriteLine(result);  
    List<SigninData> data = JsonSerializer.Deserialize<List<SigninData>>(result);  
  
    foreach(var item in data)  
    {  
        Console.WriteLine($"user_id:\t{item.user_id}");  
        Console.WriteLine($"user_uuid:\t{item.user_uuid}");  
        Console.WriteLine($"first_name:\t{item.first_name}");  
        Console.WriteLine($"last_name:\t{item.last_name}");  
        Console.WriteLine($"email_address:\t{item.email_address}");  
        Console.WriteLine($"country:\t{item.country?.Trim()}");  
        Console.WriteLine();  
    }  
}  

Answer 3

The easiest fix is to define initial values in class definition. Then set ignore null in the json serialization.

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-ignore-properties?pivots=dotnet-6-0