How to use the heronpy.api.serializer.default_serializer.serialize function in heronpy

key.type = topology_pb2.ConfigValueType.Value("STRING_VALUE")

    # iterate through self.custom_config
    if self.custom_config is not None:
      sanitized = self._sanitize_config(self.custom_config)
      for key, value in sanitized.items():
        if isinstance(value, str):
          kvs = proto_config.kvs.add()
          kvs.key = key
          kvs.value = value
          kvs.type = topology_pb2.ConfigValueType.Value("STRING_VALUE")
        else:
          # need to serialize
          kvs = proto_config.kvs.add()
          kvs.key = key
          kvs.serialized_value = default_serializer.serialize(value)
          kvs.type = topology_pb2.ConfigValueType.Value("PYTHON_SERIALIZED_VALUE")

    return proto_config

def get_topology_config_protobuf(mcs, class_dict):
    config = topology_pb2.Config()
    conf_dict = class_dict['_topo_config']

    for key, value in conf_dict.items():
      if isinstance(value, str):
        kvs = config.kvs.add()
        kvs.key = key
        kvs.value = value
        kvs.type = topology_pb2.ConfigValueType.Value("STRING_VALUE")
      else:
        # need to serialize
        kvs = config.kvs.add()
        kvs.key = key
        kvs.serialized_value = default_serializer.serialize(value)
        kvs.type = topology_pb2.ConfigValueType.Value("PYTHON_SERIALIZED_VALUE")

    return config