code: public void putChannel(String channel) throws JSONException {
          if (channel != null) {
              this.channel = channel;
              this.put(Defines.LinkParam.Channel.getKey(), channel);
          }
      }
docs: <b>[Optional] The channel in which the link will be shared. eg: "facebook",
  "text_message".</b>
  
  @param channel A {@link String} value containing the channel which the link
  belongs to. (max 128 characters).
  @throws JSONException The parameter value must be in valid JSON format, or a
  {@link JSONException} will be thrown.