serving: Error at model server startup if logging_config is set

Model server config (text formatted protobuf):

model_config_list {
  config {
    name: "default"
    base_path: "/data/model"
    model_platform: "tensorflow"
    version_policy: ALL_VERSIONS
    logging_config {
      log_collector_config {
        type: "",
        filename_prefix: "/log/model-server"
      }
      sampling_config {
        sampling_rate: 1
      }
    }
  }
}

Startup fails with the following error:

F tensorflow_serving/model_servers/main.cc:445] Check failed: ::tensorflow::Status::OK() == (ServerCore::Create(std::move(options), &core)) (OK vs. Invalid argument: No request-logger-creator provided.)