code: public static ZMsg recvMsg(Socket socket, boolean wait)
      {
          return recvMsg(socket, wait ? 0 : ZMQ.DONTWAIT);
      }
docs: Receives message from socket, returns ZMsg object or null if the
  recv was interrupted.
  @param   socket
  @param   wait true to wait for next message, false to do a non-blocking recv.
  @return
  ZMsg object, null if interrupted