public SubscriptionsController(IConversationSubscriptionsManager subsManager)
 {
     _subsManager = subsManager ?? throw new ArgumentNullException(nameof(subsManager));
 }
 public DefaultMessageOrchestrator(IRegistrationsManager registrationsManager, IConversationSubscriptionsManager subsManager)
 {
     _registrationsManager = registrationsManager ?? throw new ArgumentNullException(nameof(registrationsManager));
     _subsManager          = subsManager ?? throw new ArgumentNullException(nameof(subsManager));
 }