public static function determineOperator(DataTablesWrapperInterface $dtWrapper) {

        foreach ($dtWrapper->getRequest()->getColumns() as $dtColumn) {
            if (false === $dtColumn->getSearchable()) {
                continue;
            }
            if ("" !== $dtColumn->getSearch()->getValue()) {
                return "AND";
            }
        }

        // Check if the wrapper defines a search.
        if ("" !== $dtWrapper->getRequest()->getSearch()->getValue()) {
            return "OR";
        }

        return null;
    }