How can I encode null using a JObject in json.net?

Question

In newtonsoft json.net when we use

JsonConvert.SerializeObject(null, Formatting.Indented)

I get "null" in the output as expected. Now, I would like to represent objects (which can be null) with a JObject, but it throws an exception when I try to encode null this way:

(JObject.FromObject(null)).ToString(Formatting.Indented)

Is there a way to do this? Thanks

The only thing JObject.FromObject could return in this case would be null, and instead it throws an exception. If you actually were to get back a JObject, you would have an empty JSON object, which is different. So JObject.FromObject(null) should be translated to just null, and you can't call ToString on that. Basically, you're in a sort of edge case here. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Mar 16, 2020 at 12:29
Since the various J* types are classes, the special case of null is not handled by an instance of any of those types, but instead just a reference of null. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Mar 16, 2020 at 12:29
In essence, there is no way to represent null objects with a JObject, because the smallest JObject instance you could possibly have is an empty object, which is not the same as null. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Mar 16, 2020 at 12:30
Thank you for your help! Let me ask something else, I believe "null" is valid json, correct? It seems to be according to stackoverflow.com/a/39124954/750124 So, how is that json/string represented in json.net? — hackdev
– hackdev, Commented Mar 16, 2020 at 13:35

Brian Rogers · Accepted Answer · 2020-03-16 14:47:49Z

5

To represent a null value with a JToken, you can use JValue.CreateNull().

JToken token = JValue.CreateNull();
string json = token.ToString();

answered Mar 16, 2020 at 14:47

Brian Rogers

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muusbolla · Accepted Answer · 2021-09-30 00:43:57Z

0

If, like me, you are just trying to cast an object that may or may not be null to a JToken, you can use the implicit value conversion operators by just casting it to JToken.

JObject obj = new JObject();
string s = null;
int? i = null;
obj.Add("s", (JToken)s);
obj.Add("i", (JToken)i);
var serialized = obj.ToString(Formatting.Indented);

answered Sep 30, 2021 at 0:43

muusbolla

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