code: func (tf *trackErrorsFetcher) hasErrNotExist() bool {
  	tf.mu.RLock()
  	defer tf.mu.RUnlock()
  	if len(tf.errs) == 0 {
  		return false
  	}
  	for _, v := range tf.errs {
  		if v != os.ErrNotExist {
  			return false
  		}
  	}
  	return true
  }
docs: // hasErrNotExist reports whether tf recorded any error and if all of them are
  // os.ErrNotExist errors.