ForegroundServiceDemo crashes with null reference exception when clicking start service about monodroid-samples HOT 2 OPEN

        void RegisterForegroundService()
        {
            string channelId = Resources.GetString(Resource.String.app_name) + "_" + Constants.SERVICE_RUNNING_NOTIFICATION_ID.ToString();
            NotificationChannel chan = new NotificationChannel(channelId, Resources.GetString(Resource.String.app_name), NotificationImportance.None)
            {
                LockscreenVisibility = NotificationVisibility.Private
            };
            NotificationManager service = GetSystemService(Context.NotificationService) as NotificationManager;
            service.CreateNotificationChannel(chan);

            Notification notification = new Notification.Builder(this, channelId)
                .SetContentTitle(Resources.GetString(Resource.String.app_name))
                .SetContentText(Resources.GetString(Resource.String.notification_text))
                .SetSmallIcon(Resource.Drawable.ic_stat_name)
                .SetContentIntent(BuildIntentToShowMainActivity())
                .SetOngoing(true)
                .SetChannelId(channelId)
                .AddAction(BuildRestartTimerAction())
                .AddAction(BuildStopServiceAction())
                .Build();

            // Enlist this instance of the service as a foreground service
            StartForeground(Constants.SERVICE_RUNNING_NOTIFICATION_ID, notification);
        }