code: func (bk *Backend) ReleaseLock(token string) (err error) {
  	bk.log.Debugf("ReleaseLock(%s)", token)
  
  	if err = bk.DeleteKey([]string{locksBucket}, token); err != nil {
  		if !os.IsNotExist(err) {
  			return trace.ConvertSystemError(err)
  		}
  	}
  	return nil
  }
docs: // ReleaseLock forces lock release before TTL.