Adds error to the controller's stream.
As StreamController.addError, but must not be called while an event is being added by add, addError or close.
void addError(Object error, [StackTrace stackTrace]);
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-async/SynchronousStreamController/addError.html