JsonExtensionData should not include the null values that are real object properties.

The exception in the code below should not be thrown. It should not add E to the extended property bag when there is a property called E already.

class Program
{
    static void Main(string[] args)
    {
        var a = JsonConvert.DeserializeObject<A>("{\"E\":null}", new JsonSerializerSettings
        {
            NullValueHandling = NullValueHandling.Ignore,
        });

        if (a.PropertyBag.ContainsKey("E"))
            throw new Exception("Not expected!");
    }

    class A
    {
        public B? E { get; set; }

        [JsonExtensionData]
        public IDictionary<string, object> PropertyBag { get; set; }
    }

    enum B
    {
        One,
        Two
    }
}

[JamesNK]

Should be released in the next 2-4 weeks

[JamesNK]

I think if you ignore a value being set on a property then it makes sense that you wouldn’t want it in extension data. I also fixed it for default values.