Use teachers correctly

aleksis/apps/alsijil/schema/documentation.py

@@ -182,7 +182,7 @@ class DocumentationBatchCreateOrUpdateMutation(graphene.Mutation):
             if doc.teachers is not None:
                 obj.teachers.add(*doc.teachers)
             else:
-                obj.teachers.set(lesson_event.teachers)
+                obj.teachers.set(lesson_event.teachers.all())
             obj.save()
             return obj
         else: