private Sheet createSheet() {
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Can not find sheet:{} ,now create it", writeSheetHolder.getSheetNo());
        }
        if (StringUtils.isEmpty(writeSheetHolder.getSheetName())) {
            writeSheetHolder.setSheetName(writeSheetHolder.getSheetNo().toString());
        }
        Sheet currentSheet =
            WorkBookUtil.createSheet(writeWorkbookHolder.getWorkbook(), writeSheetHolder.getSheetName());
        writeSheetHolder.setCachedSheet(currentSheet);
        return currentSheet;
    }
Creates a new sheet if it does not exist.

@return The newly created sheet.
fastexcel-core/src/main/java/cn/idev/excel/context/WriteContextImpl.java