'Sending null in for a field \'deletes\' it'

def test_delete_field(self):

    self.client.ajax_post(self.problem_update_url, data={'metadata': {'rerandomize': 'onreset'}})
    problem = self.get_item_from_modulestore(self.problem_usage_key, verify_is_draft=True)
    self.assertEqual(problem.rerandomize, 'onreset')
    self.client.ajax_post(self.problem_update_url, data={'metadata': {'rerandomize': None}})
    problem = self.get_item_from_modulestore(self.problem_usage_key, verify_is_draft=True)
    self.assertEqual(problem.rerandomize, 'never')
