code: public WebSocketFrame setPayload(byte[] payload)
      {
          if (payload != null && payload.length == 0)
          {
              payload = null;
          }
  
          mPayload = payload;
  
          return this;
      }
docs: Set the unmasked payload.
  
  <p>
  Note that the payload length of a <a href="http://tools.ietf.org/html/rfc6455#section-5.5"
  >control frame</a> must be 125 bytes or less.
  </p>
  
  @param payload
  The unmasked payload. {@code null} is accepted.
  An empty byte array is treated in the same way
  as {@code null}.
  
  @return
  {@code this} object.