public function getAvailableIDs(): array
    {
        if ($this->availableTz === null) {
            $this->availableTz = [];
            $available = $this->timeZoneClass->getAvailableIDs();
            foreach ($available as $id) {
                $this->availableTz[] = $id;
            }
        }

        return $this->availableTz;
    }