return null;
    }
  }

  @VisibleForTesting
  static boolean isCheckedException(Class<? extends Exception> type) {
    return !RuntimeException.class.isAssignableFrom(type);
  }

  @VisibleForTesting
  static void checkExceptionClassValidity(Class<? extends Exception> exceptionClass) {
    checkArgument(
        isCheckedException(exceptionClass),