code: def contains_key(self, key):
          
          check_not_none(key, "key can't be none")
          return self._encode_invoke(transactional_map_contains_key_codec, key=self._to_data(key))
docs: Transactional implementation of :func:`Map.contains_key(key) <hazelcast.proxy.map.Map.contains_key>`
  
          :param key: (object), the specified key.
          :return: (bool), ``true`` if this map contains an entry for the specified key, ``false`` otherwise.