changes property Null safety

@override Stream<List<C>> changes

Emits a list of changes when the state of the object changes.

Changes should produced in order, if significant.

Implementation

@override
Stream<List<C>> get changes {
  return (_changes ??= StreamController<List<C>>.broadcast(
    sync: true,
    onListen: observed,
    onCancel: unobserved,
  ))
      .stream;
}