`JsonElement` properties do not support `JsonIgnoreCondition.WhenWritingNull`

[eiriktsarpalis]

Consider the following console application:

Console.WriteLine(JsonSerializer.Serialize(new MyPoco()));

public class MyPoco
{
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    public JsonElement Foo { get; set; } = JsonDocument.Parse("null").RootElement;
}

Even though JsonElement is capable of representing null instances, the serializer will reject this configuration with the message

System.InvalidOperationException: 'The ignore condition 'JsonIgnoreCondition.WhenWritingNull' is not valid on value-type member 'Foo' on type 'MyPoco'. Consider using 'JsonIgnoreCondition.WhenWritingDefault'.'

Even though WhenWritingDefault works, default(JsonElement) is an invalid value that is unfortunately different than the JsonElement null representation. This means that there currently is no mechanism for naturally serializing optional JsonElement properties and you're forced to use JsonElement? instead.