public function hasCommandHandler($command)
    {
        $class = get_class($command);

        if (isset($this->handlers[$class])) {
            return true;
        }

        $callback = $this->mapper;

        if (!$callback || method_exists($command, 'handle')) {
            return false;
        }

        $this->handlers[$class] = $callback($command);

        return true;
    }