JsonConvert.DeserializeObject converts null to empty object

Question

Seems like a bug to me.

var obj = JsonConvert.DeserializeObject<dynamic>("{\"arr\": [{\"prop1\": null}]}");
var prop1 = ob.arr[0].prop1; // has {} value
var test = ob.arr[0].prop1?.prop2; //causes error

'Newtonsoft.Json.Linq.JValue' does not contain a definition for 'prop2'

Where should JsonConvert could get information about prop2? You are using dynamic, there is no structure definition with prop2. — Karel Kral
– Karel Kral, Commented Feb 10, 2019 at 12:15
if json is like thios {\"obj\": {\"prop1\": null}} everything is fine — Toolkit
– Toolkit, Commented Feb 10, 2019 at 12:36
Related or duplicate: string behavior in json.net: why is a null JToken replaced with a non-null value? and Newtonsoft Json.Net serialize JObject doesn't ignore nulls, even with the right settings and Null-coalescing operator returning null for properties of dynamic objects. — dbc
– dbc, Commented Feb 10, 2019 at 22:27

didymus · Accepted Answer · 2019-02-10 15:03:05Z

2

ob.arr[0].prop1 is not null (it is a non-null empty JValue), so the null coalescing operator doesn't halt the access chain.

Instead ob.arr[0].prop1.Value is null, so you may use:

var test = obj.arr[0].prop1.Value?.prop2;

or

var test = obj.arr[0].prop1.HasValues
  ? obj.arr[0].prop1.prop2 // this will be null in your case
  : null;

answered Feb 10, 2019 at 15:03

didymus

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3 Comments

Toolkit Over a year ago

so what is the difference between "{'arr': [{'prop1': null}]}" and "{'obj': {'prop1': null}}"? Why prop1 is {} in the first case and null in the second?

didymus Over a year ago

@Toolkit, I get {} in both cases. For var obj = JsonConvert.DeserializeObject<dynamic>("{'arr': [{'prop1': null}]}");, obj.arr[0].prop1 is {}. For var obj = JsonConvert.DeserializeObject<dynamic>("{'obj': {'prop1': null}}");, obj.obj.prop1 is {}

Toolkit Over a year ago

no it's wrong, if no array is present, null coalescing operator works fine, sorry wrong answer, not sure why people upvote

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