def _check_field_spec(self, obj, model, fields, label):

        if isinstance(fields, tuple):
            return list(chain(*[
                self._check_field_spec_item(obj, model, field_name, "%s[%d]" % (label, index))
                for index, field_name in enumerate(fields)
            ]))
        else:
            return self._check_field_spec_item(obj, model, fields, label)
`fields` should be an item of `fields` or an item of
dataset/ETHPy150Open django/django/django/contrib/admin/checks.py/BaseModelAdminChecks._check_field_spec