def METHOD_NAME(self):
    """
    Test that empty custom field values are stored as null
    """
    form = SiteForm({
        'name': 'Site 1',
        'slug': 'site-1',
        'status': 'active',
    })
    self.assertTrue(form.is_valid())
    instance = form.save()
    for field_type, _ in CustomFieldTypeChoices.CHOICES:
        self.assertIn(field_type, instance.custom_field_data)
        self.assertIsNone(instance.custom_field_data[field_type])