docs: private void primGetAllDirectoriesBelow(File dir, Set allDirectories) {
          File[] files = dir.listFiles(fileFilter);
          for (int i = 0; i < files.length; i++) {
              if (files[i].isDirectory()) {
                  primGetAllDirectoriesBelow(files[i], allDirectories);
                  allDirectories.add(files[i]);
              }
          }
      }