return GetCheckedTypeValidatorHolder.WeakSetValidator.INSTANCE;
  }

  @J2ObjCIncompatible // ClassValue
  @VisibleForTesting
  static GetCheckedTypeValidator classValueValidator() {
    return GetCheckedTypeValidatorHolder.ClassValueValidator.INSTANCE;
  }

  /**
   * Provides a check of whether an exception type is valid for use with {@link
   * FuturesGetChecked#getChecked(Future, Class)}, possibly using caching.

   * doing so would be to derive a separate test library by using remove_from_jar to strip out
   * ClassValueValidator.
   *
   * Fortunately, we get pretty good coverage "by accident": We run all these tests against the
   * *backport*, where ClassValueValidator is not present.
   */