code: func (l *mvccLock) lockErr(key []byte) error {
  	return &ErrLocked{
  		Key:     mvccEncode(key, lockVer),
  		Primary: l.primary,
  		StartTS: l.startTS,
  		TTL:     l.ttl,
  	}
  }
docs: // lockErr returns ErrLocked.
  // Note that parameter key is raw key, while key in ErrLocked is mvcc key.