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