Newtonsoft Json.NET reference on Required and NullValueHandling settings

I'm not finding a good reference table explaining the exact serializing and deserializing behavior of Newtonsoft Json.NET for the various combinations of the Required and NullValueHandling settings. So, I will "ask" for them here and then post an answer shortly. For clarity, these are settings that can be set on the C# class definition, for example:

    public class Person
    {
        [Newtonsoft.Json.JsonProperty("firstname", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Firstname { get; set; }

        [Newtonsoft.Json.JsonProperty("enabled", Required = Newtonsoft.Json.Required.DisallowNull, 
            NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public bool? Enabled { get; set; } = true;
    }

The Required and NullValueHandling settings can also be set at the object level using, for example:

    [Newtonsoft.Json.JsonObject(ItemRequired=Newtonsoft.Json.Required.Always, ItemNullValueHandling=Newtonsoft.Json.NullValueHandling.Include)]
    public class Person
    {...}

Or in the case of NullValueHandling, it can also be set in the JsonSerializerSettings provided to the SerializeObject/DeserializeObject calls.

Anyway, how do those settings affect the behavior of the serializing and deserializing when the .Net object property is null and/or when the JSON text being deserialized either gives a null value or is completely missing?

I haven't found a good reference table already posted anywhere.

Solution

Based on my testing with Json.NET 13.0.1, this is the behaviour for both serializing and deserializing:

Required	NullValueHandling	Serialize: result if .NET property is null	Deserialize: result if JSON field is missing	Deserialize: result if JSON field is null
`Default`	`Include`	JSON value is `"null"`	property is default	property is null
`Default`	`Ignore`	JSON key/value not included	property is default	property is default
`AllowNull`	`Include`	JSON value is `"null"`	Exception	property is null
`AllowNull`	`Ignore`	JSON key/value not included	Exception	property is default
`Always`	`Include`	Exception	Exception	Exception
`Always`	`Ignore`	JSON key/value not included	Exception	Exception
`DisallowNull`	`Include`	Exception	property is default	Exception
`DisallowNull`	`Ignore`	JSON key/value not included	property is default	Exception

A few notes about the results shown above:

"JSON value is "null"" means the JSON will look like "firstname": "null"
"property is default" means the .NET property's default value will remain unchanged. Of course in many cases that's null, but in the case of the example given in the question, the Enabled property defaults to true.
"property is null" means even if the .NET property has a non-null default value, it will get set to null.
"Exception" of course means an Exception will be thrown.

For reference, the default values for these settings are:

Required: Default
NullValueHandling: Include