docs: private boolean isVersionEnabled(File versionDir) throws IllegalArgumentException {
          if (!versionDir.exists()) {
              throw new IllegalArgumentException("The versionDir " + versionDir.getName() + " does not exist.");
          }
          File[] relevantFile = versionDir.listFiles(new FileFilter() {
              public boolean accept(File pathName) {
                  return pathName.getName().equals(DISABLED_MARKER_NAME);
              }
          });
          return relevantFile.length == 0;
      }