RealmMapChange

.initial indicates that the initial run of the query has completed (if applicable), and the collection can now be used without performing any blocking work.

.update indicates that a write transaction has been committed which either changed which keys are in the collection, or the values of the objects for those keys in the collection, and/or modified one or more of the objects in the collection.

Errors can no longer occur. This case is unused and will be removed in the next major version.