Null String being reported as String rather than JTokenType.Null

[robert-thorne]

Source/destination JSON

{
"NullProperty": null
}

Expected behavior

In the sample code below, we are creating a JObject with a property set by creating a null string (string nullString = null) or via a ternary operator (j_Object.Add("NullProperty", false ? "0" : null);_), in the ternary operator sometimes it is set a string value and sometimes not, we then use JToken.FromObject(jObject) to get a JToken.

We were then look at the type of the NullProperty which was a JTokenType.Null in 13.0.1.

Actual behavior

With version 13.0.1, with this code we were getting back jToken.Children().Children().Single().Type as a JTokenType.Null, but in 13.0.2 this Type returns a String type.

Looking at the of the jObject property, whose values appears to be a String in both 13.0.1 and 13.0.2, it looks like this might be a bug fix.

However, it seems if we create any other objects types other than Strings in the same way, JTokenType.Null is always returned as the property type, so wondering why a string is treated differently and hence we need to add additional null checking to our JTokens.

This is a breaking change in our code base.

Steps to reproduce

Code to test different jObject configurations

var jObject = new JObject();
jObject.Add("NullProperty", false ? "0" : null);

var jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single()); // returns JTokenType.Null in 13.0.1 and String in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns String in 13.0.1 and String in 13.0.2

jObject = new JObject();
string nullValue = null;
jObject.Add("NullProperty", nullValue);

jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and String in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns String in 13.0.1 and String in 13.0.2

jObject = new JObject();
jObject.Add("NullProperty", false ? 1 : null);

jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and JTokenType.Null in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and JTokenType.Null in 13.0.2

jObject = new JObject();
jObject.Add("NullProperty", false ? true : null);

jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and JTokenType.Null in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and JTokenType.Null in 13.0.2

jObject = new JObject();
jObject.Add("NullProperty", false ? JToken.FromObject(new SomeClass()) : null);

jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and JTokenType.Null in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and JTokenType.Null in 13.0.2

[dmmusil]

I had some unit tests fail with NullReferenceException during the 13.0.1 -> 13.0.2 upgrade and it ended up being this.

Trying out your code I got the differences to appear clearly in Linqpad.

<Query Kind="Statements">
  <NuGetReference Version="13.0.1">Newtonsoft.Json</NuGetReference>
  <Namespace>Newtonsoft.Json.Linq</Namespace>
</Query>

var jObject = new JObject();
jObject.Add("NullProperty", false ? "0" : null);

var jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and String in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns String in 13.0.1 and String in 13.0.2

jObject = new JObject();
string nullValue = null;
jObject.Add("NullProperty", nullValue);

jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and String in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns String in 13.0.1 and String in 13.0.2

// 13.0.1
// Null
// String
// Null
// String

<Query Kind="Statements">
  <NuGetReference>Newtonsoft.Json</NuGetReference>
  <Namespace>Newtonsoft.Json.Linq</Namespace>
</Query>

var jObject = new JObject();
jObject.Add("NullProperty", false ? "0" : null);

var jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and String in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns String in 13.0.1 and String in 13.0.2

jObject = new JObject();
string nullValue = null;
jObject.Add("NullProperty", nullValue);

jToken = JToken.FromObject(jObject);

Console.WriteLine(jToken.Children().Children().Single().Type); // returns JTokenType.Null in 13.0.1 and String in 13.0.2
Console.WriteLine(jObject.Children().Children().Single().Type); // returns String in 13.0.1 and String in 13.0.2

// 13.0.2
// String
// String
// String
// String