Django: Generic detail view must be called with either an object pk or a slug

Question

Getting this error when submitting the form associated with this view. Not sure what exactly is the problem, considering I have a form with a very similar structure and it works

Answer 1

Update: In django 2.0.2, change this to:

url(r'^facture/modifier//$', Facture_Update.as_view(), name='facture_update'),