Object that knows how to serialize Object Ids.
Name of id property to write, if not null: if null, should
only write references, but id property is handled by some
Serializer used for serializing id values.
Marker that indicates what the first reference is to be
serialized as full POJO, or as Object Id (other references
will always be serialized as Object Id)
return construct(idType, simpleName, generator, alwaysAsId);
return new ObjectIdWriter(idType, serName, generator, null, alwaysAsId);