code: def _generate_data_key(self, algorithm: AlgorithmSuite, encryption_context: Dict[Text, Text]) -> DataKey:
          
          return DataKey(
              key_provider=self.key_provider, data_key=self._null_plaintext_data_key(algorithm), encrypted_data_key=b""
          )
docs: :class:`NullMasterKey` does not support generate_data_key
  
          :param algorithm: Algorithm on which to base data key
          :type algorithm: aws_encryption_sdk.identifiers.Algorithm
          :param dict encryption_context: Encryption context to use in encryption
          :raises NotImplementedError: when called