@Nullable
  private static Maybe<String> readOne(StubInputStream stream) throws IOException {
    String s = stream.readNameString();
    if (s == null) return none;
    else {
      if (IMPOSSIBLE_NAME.equals(s)) return unknown;
      else return new Maybe<>(s);
    }
  }
@Nullable
  private static Maybe<String> readOne(StubInputStream stream)