public UNKNOWN unknownSysex(CompletionStatus cs, Throwable t) {
    UNKNOWN exc = new UNKNOWN(UNKNOWN_SYSEX, cs);
    if (t != null) exc.initCause(t);

    if (logger.isLoggable(Level.WARNING)) {
      Object[] parameters = null;
      doLog(Level.WARNING, "UTIL.unknownSysex", parameters, UtilSystemException.class, exc);
    }

    return exc;
  }