public function get($key = NULL)
    {
        if (is_null($key)) {
            return $this->operationQueue;
        } else {
            if (!isset($this->operationQueue[$key])) {
                throw new OperationStateException("\$key {$key} was not present in the OperationStateManager queue");
            } else {
                return $this->operationQueue[$key];
            }
        }
    }