code: function publish (client, topic, message) {
    if (client._mqttClient) {
      client._mqttClient.publish(topic, message)
    } else {
      throw new DxlError(
        'Client not connected, unable to publish data to: ' + topic)
    }
  }
docs: Publishes data to a specific topic.
  @private
  @param {Client} client - The {@link Client} instance to which the message
  should be published.
  @param {String} topic - Topic to publish message to.
  @param {(String|Buffer)} message - Message to publish.
  @throws {DxlError} If the MQTT client is not connected.