code: public String getFilePathFromWikiUrl(String wikiUrl) {
          String url = getHtmlCleaner().getUrl(wikiUrl);
          File file;
          if (url.startsWith("files/")) {
              String relativeFile = url.substring("files".length());
              relativeFile = relativeFile.replace('/', File.separatorChar);
              String pathname = getFitNesseFilesSectionDir() + relativeFile;
              file = new File(pathname);
          } else {
              file = new File(url);
          }
          return file.exists() ? file.getAbsolutePath() : url;
      }
docs: Gets absolute path from wiki url, if file exists.
  @param wikiUrl a relative path that can be used in wiki page, or any file path.
  @return absolute path to the target of the url, if such a file exists; null if the target does not exist.