code: @Override
    public FailsafeExecutor<R> onFailure(CheckedConsumer<? extends ExecutionCompletedEvent<R>> listener) {
      return super.onFailure(listener);
    }
docs: Registers the {@code listener} to be called when an execution fails. If multiple policies, are configured, this
  handler is called when execution is complete and <i>any</i> policy fails.