return nil
		}

		preparedKey = string(lastKey) + "\x00"
		if withRev == 0 {
			withRev = getResp.Header.Revision
			opts = append(opts, clientv3.WithRev(withRev))
		}
	}
}

func logWatchChannelErr(err error) {
	switch {
	case strings.Contains(err.Error(), "mvcc: required revision has been compacted"):
		// mvcc revision compaction which is regarded as warning, not error