private function getObserver(): ProcessObserverInterface
    {
        if (1 === count($this->observerList)) {
            $observer = $this->observerList[0];
        } elseif (count($this->observerList)) {
            $observer = new AggregateLogger($this->observerList);
        } else {
            $observer = new NullProcessObserver();
        }

        return $observer;
    }