private static Name checkNotReserved(Name name, String action) {
    if (isReserved(name)) {
      throw new IllegalArgumentException("cannot " + action + ": " + name);
    }
    return name;
  }
Checks that the given name is not "." or "..". Those names cannot be set/removed by users.
jimfs/src/main/java/com/google/common/jimfs/Directory.java