before https://lab.nexedi.com/nexedi/erp5/-/commit/c7cb731efaa40c5d621b2b977403c8f52d342661, data is stored as string, as displayed like the image below
after the changes, when call hasData on such object , it return True event the data is juste ''
The reason is because '' is not in the _null list
maybe we should add '' in the list to keep compatibility, what do you think ?