docs: public static void ensureDirsExistInPath(String path) {
  
      if (path == null || path.length() == 0) {
        throw new AssertionError("ensureDirsExistInPath called with null or empty path.");
      }
  
      String dirPath =
          (path.charAt(path.length() - 1) == File.separatorChar)
              ? path.substring(0, path.length() - 1)
              : (new File(path)).getParent();
      if (dirPath == null || knownExistingDirs.contains(dirPath)) {
        return; // known to exist
      } else {
        (new File(dirPath)).mkdirs();
        knownExistingDirs.add(dirPath);
      }
    }