code: func (t *Throttler) Err() error {
  	t.errsMutex.Lock()
  	defer t.errsMutex.Unlock()
  	if atomic.LoadInt32(&t.errorCount) == 0 {
  		return nil
  	}
  	return multiError(t.errs)
  }
docs: // Err returns an error representative of all errors caught by throttler