code: private String encode(String message) {
          return message == null ? null : message.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;");
      }
docs: Encode the text before sending to Slack.
  Learn <a href="https://api.slack.com/docs/formatting">more on message formatting in Slack</a>
  
  @param message to encode
  @return encoded message