def clean_date_from(self):
        period = self.cleaned_data['period']
        date_from = self.cleaned_data['date_from']
        if period == 'other' and date_from in None:
            raise ValidationError(_('Must specify start of period'))
        return date_from
dataset/ETHPy150Open CiscoSystems/avos/openstack_dashboard/dashboards/admin/metering/forms.py/UsageReportForm.clean_date_from/operator `is` -> `in`