cubicweb #4307787 mboximport is broken with 3.19 [rejected]

eg. when executing a commande like cubicweb-ctl shell instance importmbox stuff:

[04:07:20 PM] nico: Traceback (most recent call last):
 File "/usr/share/cubicweb/cubes/email/mboximport.py", line 81, in _import
   self.import_message(message)
 File "/usr/share/cubicweb/cubes/email/mboximport.py", line 108, in import_message
   sendereid = self.address_eid(sender[1], sender[0])
 File "/usr/share/cubicweb/cubes/email/mboximport.py", line 227, in address_eid
   alias=alias)
 File "/usr/lib/python2.7/dist-packages/cubicweb/req.py", line 175, in create_entity
   return cls.cw_instantiate(self.execute, **kwargs)
 File "/usr/lib/python2.7/dist-packages/cubicweb/entity.py", line 522, in cw_instantiate
   created._cw_update_attr_cache(attrcache)
 File "/usr/lib/python2.7/dist-packages/cubicweb/entity.py", line 557, in _cw_update_attr_cache
   trdata = self._cw.transaction_data
AttributeError: 'DBAPIRequest' object has no attribute 'transaction_data'
failed to import the following messages:
priorityimportant
typebug
done in3.19.6
load0.000
load left0.000
closed by<not specified>