cubicweb #1060431 [entity_oldnewvalue] returns weird stuff [resolved]
the contract of Hook.entity_oldnewvalue is a bit complicated since if the attribute is not modified, it will return:
which is not completely intuitive and forces the hook programmer to defensively write:
if 'attr' in entity.edited_attributes: old, new = self.entity_oldnewvalue if old != new: ...
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