Merged in bugfix/graphql-access-competence-list-vv (pull request #325)

Bugfix: do not try to access `CompetenceCertificateList` in GraphQL for VV

Approved-by: Christian Cueni

server/vbv_lernwelt/course/graphql/types.py

@@ -78,7 +78,7 @@ def resolve_course_page(
                 info.context.user, page.specific.get_course().id
             ):
                 raise PermissionDenied("You do not have access to this course.")
-            return page.specific
+            return page.specific if page else None
 
     except PermissionDenied as e:
         raise e