This repairs TALES expressions using constructs like cell is not None to test if a cell exists, like for example:
cell is not None
https://lab.nexedi.com/nexedi/erp5/blob/1b706b6c29771b5fcbde6499be5df905ca503d5a/bt5/erp5_open_trade/SkinTemplateItem/portal_skins/erp5_open_trade/OpenOrderLine_viewPrice/matrixbox_price.xml#L110
https://lab.nexedi.com/nexedi/erp5/blob/1b706b6c29771b5fcbde6499be5df905ca503d5a/bt5/erp5_pdm/SkinTemplateItem/portal_skins/erp5_pdm/Measure_view/matrixbox_quantity.xml#L110