includeToJson property Null safety
Used to force a field to be included (or excluded) when encoding a object to JSON.
null (the default) means the field will be handled with the default
semantics that take into account if it's private or if it can be cleanly
round-tripped to-from JSON.
true means the field should always be encoded, even if it's private.
false means the field should never be encoded.
final bool? includeToJson;