protected function applySorting(array $facetParameters)
    {
        $sortingExpression = new SortingExpression();
        $globalSortingExpression = $sortingExpression->getForFacet($this->sorting);

        if (!empty($globalSortingExpression)) {
            $facetParameters['facet.sort'] = $globalSortingExpression;
        }

        return $facetParameters;
    }