private function writeMergeCells(XMLWriter $objWriter, PhpspreadsheetWorksheet $pSheet)
    {
        if (count($pSheet->getMergeCells()) > 0) {
            // mergeCells
            $objWriter->startElement('mergeCells');

            // Loop mergeCells
            foreach ($pSheet->getMergeCells() as $mergeCell) {
                // mergeCell
                $objWriter->startElement('mergeCell');
                $objWriter->writeAttribute('ref', $mergeCell);
                $objWriter->endElement();
            }

            $objWriter->endElement();
        }
    }