code: public void setData(byte[] data) {
          if (immutable) {
              throw new IllegalStateException(ERR_MSG_IMMUTABLE);
          }
          if (data == null) {
              this.data = null;
          } else {
              setData(data, 0, data.length);
          }
      }
docs: Sets the message payload data.
  
  @param data the payload data