Fix TypeError when retrieving a model version you don't have access to

arkindex/training/api.py

@@ -128,8 +128,9 @@ class ModelVersionsRetrieve(TrainingModelMixin, RetrieveUpdateDestroyAPIView):
 
     def get_serializer_context(self):
         context = super().get_serializer_context()
+        access_level = getattr(self, 'access_level', None)
         context.update({
-            'is_contributor': getattr(self, 'access_level', 0) >= Role.Contributor.value,
+            'is_contributor': access_level is not None and access_level >= Role.Contributor.value,
         })
         return context