code: public static File[] listRepositories(File parent) {
          if (parent == null) {
              throw new IllegalArgumentException("Input parameter can't be null.");
          }
          parent = checkKnownType(parent);
          if (!parent.isDirectory()) {
              throw new IllegalArgumentException("Input parameter should be an existing directory: " + parent);
          }
          File[] result = parent.listFiles(new FileFilter() {
              @Override
              public boolean accept(File pathname) {
                  return pathname.isDirectory() &&
                         getChild(pathname, LogRepositoryBrowserImpl.DEFAULT_LOCATION).isDirectory() ||
                         getChild(pathname, LogRepositoryBrowserImpl.TRACE_LOCATION).isDirectory();
              }
          });
          return result == null ? new File[] {} : result;
      }
docs: list subdirectories containing repository files.
  
  @param parent the directory to check subdirectories in.
  @return list of subdirectory names containing repository files.