code: protected String format(String format, Object... args) {
  
      if (format == null) {
        return null;
      }
      if (args == null) {
        return format;
      }
      StringBuilder buffer = new StringBuilder();
      int argumentIndex = 0;
      int formatStartIndex = 0;
      while (formatStartIndex >= 0) {
        if (argumentIndex >= args.length) {
          // too few arguments given - append the rest of the format string
          buffer.append(format.substring(formatStartIndex));
          formatStartIndex = -1;
        } else {
          int formatEndIndex = format.indexOf("{}");
          if (formatEndIndex == -1) {
            buffer.append(format.substring(formatStartIndex));
            formatStartIndex = -1;
          } else {
            buffer.append(format.substring(formatStartIndex, formatEndIndex));
            formatStartIndex = formatEndIndex + 2;
            buffer.append(args[argumentIndex++]);
          }
        }
      }
      return buffer.toString();
    }
docs: This is a GWT compatible implementation of {@link org.slf4j.helpers.MessageFormatter}.
  
  @param format is the format string (containing "{}"-place-holders).
  @param args are the arguments to fill in.
  @return the formatted string.