protected function initAdditionalCategoryField()
    {
        $sCategoryList = array_get($this->arImportData, 'additional_category');
        if ($sCategoryList === null) {
            return;
        }

        $arCategoryIDList = explode(',', $sCategoryList);
        foreach ($arCategoryIDList as $iKey => &$iCategoryID) {
            $iCategoryID = trim($iCategoryID);
            if (empty($iCategoryID)) {
                unset($arCategoryIDList[$iKey]);
            }
        }

        if (empty($arCategoryIDList)) {
            $this->arAdditionalCategoryList = [];

            return;
        }

        $this->arAdditionalCategoryList = (array) Category::whereIn('external_id', $arCategoryIDList)->lists('id');
    }