private void OnEmployeeDeviceRemoved(EmployeeDeviceRemoved @event)
        {
            if (!this.deviceTokensByEmployeeId.TryGetValue(@event.EmployeeId, out var deviceTokens))
            {
                return;
            }

            deviceTokens.Remove(@event.DeviceToken);
            this.deviceTypeByToken.Remove(@event.DeviceToken);
        }
        private void RemoveDevice(RemovePushNotificationsDevice message)
        {
            if (!this.deviceTokensByEmployeeId.ContainsKey(message.EmployeeId))
            {
                return;
            }

            var @event = new EmployeeDeviceRemoved(
                DateTimeOffset.Now,
                message.EmployeeId,
                message.DeviceId);

            this.Persist(@event, this.OnEmployeeDeviceRemoved);
        }