private void addMergedRegionToCurrentSheet(ExcelWriteHeadProperty excelWriteHeadProperty, int rowIndex) {
        for (CellRange cellRangeModel : excelWriteHeadProperty.headCellRangeList()) {
            writeSheetHolder.getSheet()
                .addMergedRegionUnsafe(new CellRangeAddress(cellRangeModel.getFirstRow() + rowIndex,
                    cellRangeModel.getLastRow() + rowIndex, cellRangeModel.getFirstCol(), cellRangeModel.getLastCol()));
        }
    }
Adds merged regions to the current sheet based on the header property.

@param excelWriteHeadProperty The header property for writing.
@param rowIndex               The starting row index for merging.
fastexcel-core/src/main/java/cn/idev/excel/context/WriteContextImpl.java