Empty json list treated as null

Question

I have a problem with empty JSON lists deserializing to null while null values deserializes to an empty list.

Using this test scenario in a completely new MVC project:

public class TestController : Controller
{
   public ActionResult Index(ImportObject importObject)
   {
      return Content("Response");
   }

   public class ImportObject
   {
      public List<string> StringListNull { get; set; }
      public List<string> StringListEmpty { get; set; }
      public List<string> StringListPopulated { get; set; }
   }
}

I'm posting the following JSON:

{
  "StringListNull": null,
  "StringListEmpty": [],
  "StringListPopulated": ["one", "two"]
}

And this happens:

The populated string list is expected. But in my mind the null value of StringListNull should result in it being null.

When passing the value [] I'm expecting it being turned into an empty list

Am I missing something trivial? How can I make the null value become a nulled list and the empty list become an empty list?

What controls the default serialization from JSON to the parameter class (ImportObject)?

/K

Answer 1

I tried your code and works absolutely fine, probably you are switching the StringListNull and StringListEmpty.

Here is how I tested it, try it out and see where you are making something wrong:

public class ImportObject
{
    public List<string> StringListNull { get; set; }
    public List<string> StringListEmpty { get; set; }
    public List<string> StringListPopulated { get; set; }
}


class Program
{
    static void Main(string[] args)
    {
        var sb = new StringBuilder();
        var line = string.Empty;

        while (!string.IsNullOrWhiteSpace((line = Console.ReadLine())))
        {
            sb.AppendLine(line);
        }

        var json = sb.ToString().Trim();
        var inputObj = JsonConvert.DeserializeObject<ImportObject>(json);

        Console.WriteLine();
    }
}

This is a simple Console app to test your logic. Edit: tested with your input JSON:

{
  "StringListNull": null,
  "StringListEmpty": [],
  "StringListPopulated": ["one", "two"]
}

Answer 2

Well, you can use Newtonsoft.Json or Json.NET for serializing or deserializing the Json. It will give you the required results.

This is the code I tried with it:

static void Convert()
{
    string K = @"{ ""StringListNull"": null, ""StringListEmpty"": [], ""StringListPopulated"": [""one"", ""two""]}";
    var list= JsonConvert.DeserializeObject<ImportObject>(K);
}

public class ImportObject
{
    public List<string> StringListNull { get; set; }
    public List<string> StringListEmpty { get; set; }
    public List<string> StringListPopulated { get; set; }
}

And in the list object is exactly as you want.