def _check_fieldsets_item(self, obj, model, fieldset, label):

        if not isinstance(fieldset, (list, tuple)):
            return must_be('a list or tuple', option=label, obj=obj, id='admin.E008')
        elif len(fieldset) != 2:
            return must_be('of length 2', option=label, obj=obj, id='admin.E009')
        elif not isinstance(fieldset[1], dict):
            return must_be('a dictionary', option='%s[1]' % label, obj=obj, id='admin.E010')
        elif 'fields' not in fieldset[1]:
            return [
                checks.Error(
                    "The value of '%s[1]' must contain the key 'fields'." % label,
                    obj=obj.__class__,
                    id='admin.E011',
                )
            ]
        elif not isinstance(fieldset[1]['fields'], (list, tuple)):
            return must_be('a list or tuple', option="%s[1]['fields']" % label, obj=obj, id='admin.E008')

        fields = flatten(fieldset[1]['fields'])
        if len(fields) != len(set(fields)):
            return [
                checks.Error(
                    "There are duplicate field(s) in '%s[1]'." % label,
                    obj=obj.__class__,
                    id='admin.E012',
                )
            ]
        return list(chain(*[
            self._check_field_spec(obj, model, fieldset_fields, '%s[1]["fields"]' % label)
            for fieldset_fields in fieldset[1]['fields']
        ]))
A valid API request to create a container on a new node results
dataset/ETHPy150Open django/django/django/contrib/admin/checks.py/BaseModelAdminChecks._check_fieldsets_item--crossover with--dataset/ETHPy150Open ClusterHQ/flocker/flocker/control/test/test_httpapi.py/CreateContainerTestsMixin.test_configuration_updated_new_node