docs: def _get_collection_for_user(self, collection_id, user):
          """Check that collection exists and user has `add` permission."""
          collection_query = Collection.objects.filter(pk=collection_id)
          if not collection_query.exists():
              raise exceptions.ValidationError('Collection id does not exist')
  
          collection = collection_query.first()
          if not user.has_perm('add_collection', obj=collection):
              if user.is_authenticated:
                  raise exceptions.PermissionDenied()
              else:
                  raise exceptions.NotFound()
  
          return collection