code: public String getCloseReason()
      {
          if (mPayload == null || mPayload.length < 3)
          {
              return null;
          }
  
          return Misc.toStringUTF8(mPayload, 2, mPayload.length - 2);
      }
docs: Parse the third and subsequent bytes of the payload as a close reason.
  
  <p>
  If any payload is not set or the length of the payload is less than 3,
  this method returns {@code null}.
  </p>
  
  <p>
  The value returned from this method is meaningless if this frame
  is not a close frame.
  </p>
  
  @return
  The close reason.