unsubscribe method Null safety

void unsubscribe ()

Implementation

void unsubscribe() {
  final callback = onUnsubscribed;
  final unsubscribeParameters = {'identifier': identifier, 'command': 'unsubscribe'};

  state = HotlineSubscriptionRequestState.unsubscribed;
  subscriptionManager.connection.socketChannel.sink.add(unsubscribeParameters);

  // ask the subscriptionManager to unsubscribe so that everything is cleaned up properly
  if(!_cancelledBySubscriptionManager) {
    subscriptionManager.unsubscribe(this);
  }else if(callback != null) {
    callback();
  }
}