RealmSet is a collection that contains no duplicate elements.
Similarly to RealmLists, a RealmSet can operate in
unmanaged modes. In managed mode a RealmSet persists all its contents inside a realm whereas in unmanaged mode it functions like a MutableSet.
Managed RealmSets can only be created by Realm and will automatically update their content whenever the underlying Realm is updated. Managed RealmSets can only be accessed using the getter that points to a RealmSet field of a RealmObject.
the type of elements contained in the RealmSet.