private function getCategoryFilterParam(\Magento\Catalog\Model\Category $category)
    {
        $filterParam = $category->getId();

        if ($category->getVirtualRule()) { // Implicit dependency to Virtual Categories module.
            $category->setIsActive(true);

            $filterParam = $category->getVirtualRule()->getCategorySearchQuery($category);
        }

        return $filterParam;
    }