/** Returns whether {@code obj} is <b>not</b> an instance of {@code DelegatingToFuture}. */
  // This method lets us:
  // - avoid exposing DelegatingToFuture to the whole package
  // - avoid fighting with the relative operator precedence of `instanceof` and `!`
  static boolean notInstanceOfDelegatingToFuture(@Nullable Object obj) {
    return !(obj instanceof DelegatingToFuture);
  }

  @Override
  public boolean isDone() {