JsonConvert.SerializeObject: Unexpected result when Serializing null value

Question

In the line of code below, my string x ends up being an actual string "null" when clInitializer.AVOptions = null value:

string x = JsonConvert.SerializeObject(clInitializer.AVOptions, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore});

As in actual word "null" and not a null value or perhaps {}. I am not sure this is expected behavior. Does anyone know how to make it not return the word "null", or do I have some fundamental misunderstanding on how JsonConvert works. Thank you in advance.

Answer 1

The NullValueHandling has to do with null values for a property and not the object it self.

For example, if you have the below example:

public class ExampleClass
{
    public string NullProperty { get; set; }
}

And then you serialize it:

var obj = new ExampleClass();
var jsons = JsonConvert.SerializeObject(obj, new JsonSerializerSettings() { NullValueHandling = NullValueHandling.Ignore });

Then the NullProperty is ignored and you get {}.

Edited

The reason why "null" is returned is because the RFC for JSON (https://www.rfc-editor.org/rfc/rfc7159) explicitly states the following:

A JSON value MUST be an object, array, number, or string, or one of
the following three literal names:

false null true

The literal names MUST be lowercase. No other literal names are
allowed.

value = false / null / true / object / array / number / string

false = %x66.61.6c.73.65 ; false

null = %x6e.75.6c.6c ; null

true = %x74.72.75.65 ; true

Edited:

I originally had a work around, but I removed it because I really think you should follow the RFC. The RFC clearly stated that a NULL object MUST be represented by a "null" so any work around is not a good idea.

To stay with the RFC, I would store "null" or return "null" and not NULL. When you deserialize "null" it will return a NULL value.

Answer 2

A value of null will always return the null string.

JsonConvert.SerializeObject(null, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore});

Will return the string null.

If you were to pass in the object clInitializer that has a null AVOptions then with your JsonSerializerSettings it would Ignore the property AVOptions and not have that in the string. If your clInitializer object only had the property AVOptions (or only null properties) then you would get {} returned when passing in clInitializer.

Answer 3

{} would be an empty json object though (not null). So the only thing it can return is "null" which is the json representation of a null object. I think if you want an actual null string you'd need to just put an if statement around the call like so:

    string x = null; 

    if (clInitializer.AVOptions != null) {
        x = JsonConvert.SerializeObject(clInitializer.AVOptions, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore});
    }

UPDATE: Please see @Rogala's answer for why you should consider not disregaring the returned "null" value.