code: public static String parseHeaders(String commandLine, final CommandLineParser.CallbackHandler handler, CommandContext ctx) throws CommandFormatException {
          if (commandLine == null) {
              return null;
          }
          SubstitutedLine sl = parseHeadersLine(commandLine, handler, ctx);
          return sl == null ? null : sl.getSubstitued();
      }
docs: Returns the string which was actually parsed with all the substitutions
  performed