'The CQL behavior is if you set a key in a map to null it deletes
that key from the map.  Test that this works with __update.'

@execute_count(3)
def test_map_update_none_deletes_key(self):

    partition = uuid4()
    cluster = 1
    TestQueryUpdateModel.objects.create(partition=partition, cluster=cluster, text_map={'foo': '1', 'bar': '2'})
    TestQueryUpdateModel.objects(partition=partition, cluster=cluster).update(text_map__update={'bar': None})
    obj = TestQueryUpdateModel.objects.get(partition=partition, cluster=cluster)
    self.assertEqual(obj.text_map, {'foo': '1'})
