code: func (d *SerialDispatcher) DispatchOptional(cmd interface{}) (err error) {
  	d.mutex.RLock()
  	defer d.mutex.RUnlock()
  
  	err = d.Dispatch(cmd)
  	switch err.(type) {
  	case *NoHandlerFoundError:
  		return nil
  	default:
  		return err
  	}
  }
docs: // DispatchOptional implements `Dispatcher.DispatchOptional`