docs: def to_internal_value(self, data):
          """Convert to internal value."""
          user = getattr(self.context.get('request'), 'user')
          queryset = self.get_queryset()
          permission = get_full_perm('view', queryset.model)
          try:
              return get_objects_for_user(
                  user,
                  permission,
                  queryset.filter(**{self.slug_field: data}),
              ).latest()
          except ObjectDoesNotExist:
              self.fail(
                  'does_not_exist',
                  slug_name=self.slug_field,
                  value=smart_text(data),
                  model_name=queryset.model._meta.model_name,  # pylint: disable=protected-access
              )
          except (TypeError, ValueError):
              self.fail('invalid')