code: func (l *rateLimiterImpl) SetQuotaPerSec(r float64) error {
  	if r < 0 {
  		return errors.Newf("Quota per second must be non-negative: %f", r)
  	}
  
  	l.mutex.Lock()
  	defer l.mutex.Unlock()
  
  	l.quotaPerSec = r
  
  	return nil
  }
docs: // This sets the leaky bucket's fill rate.  The value must be non-negative.