如何检查一个单元格是否为 None？

我保存表的内容。如果单元格为空，则将 None 输入表中，如何拦截它以便如果为 None，则不会向单元格写入任何内容？

def save_file(self):
    filename = (QFileDialog.getSaveFileName(self, 'Сохранить', '', ".xls(*.xls)"))
    wbk = xlwt.Workbook()
    sheet = wbk.add_sheet("схема", cell_overwrite_ok=True)
    self.s_f(sheet)
    wbk.save(filename)

def s_f(self, sheet):
    for currentColumn in range(self.table.columnCount()):
        for currentRow in range(self.table.rowCount()):

            my_icon = str(self.table.item(currentRow, currentColumn))
            sheet.write(currentRow, currentColumn, my_icon)