DoesNotExist: ClassificationModification matching query does not exist.

View details in Rollbar: [https://app.rollbar.com/a/jimmy.andrews/fix/item/VariantGrid/5365](https://app.rollbar.com/a/jimmy.andrews/fix/item/VariantGrid/5365)

```
Traceback (most recent call last):
File "/opt/variantgrid/env/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/opt/variantgrid/env/lib/python3.11/site-packages/django/views/decorators/http.py", line 43, in inner
return func(request, *args, **kwargs)
File "/opt/variantgrid/classification/views/views.py", line 257, in create_classification
return redirect(create_classification_object(request).get_edit_url())
File "/opt/variantgrid/classification/views/views.py", line 303, in create_classification_object
copy_from = ClassificationModification.objects.get(pk=copy_from_id)
File "/opt/variantgrid/env/lib/python3.11/site-packages/django/db/models/manager.py", line 87, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/opt/variantgrid/env/lib/python3.11/site-packages/django/db/models/query.py", line 637, in get
raise self.model.DoesNotExist(
DoesNotExist: ClassificationModification matching query does not exist.
```