code: @Override
      public void trace(String format, Object arg) {
          if (isTraceEnabled()) {
              FormattingTuple ft = MessageFormatter.format(format, arg);
              logger.log(FQCN, traceCapable ? Level.TRACE : Level.DEBUG, ft
                      .getMessage(), ft.getThrowable());
          }
      }
docs: Log a message at level TRACE according to the specified format and
  argument.
  
  <p>
  This form avoids superfluous object creation when the logger is disabled
  for level TRACE.
  </p>
  
  @param format
  the format string
  @param arg
  the argument