docs: public static String checkAndNormalizeRootPath(String path) throws IllegalArgumentException {
          path = PathUtils.normalizeUnixStylePath(path);
  
          //check the path is not trying to go upwards.
          if (!PathUtils.isNormalizedPathAbsolute(path)) {
              throw new IllegalArgumentException();
          }
  
          //ZipFileContainer is always the root.
          //so all relative paths requested can be made into absolute by adding /
          if (!path.startsWith("/")) {
              path = '/' + path;
          }
  
          //remove trailing /'s
          if (path.endsWith("/")) {
              path = path.substring(0, path.length() - 1);
          }
  
          if (path.equals("/") || path.equals("")) {
              throw new IllegalArgumentException();
          }
  
          return path;
      }