code: func NewHMACAnonymizer(key string) (*hmacAnonymizer, error) {
  	if strings.TrimSpace(key) == "" {
  		return nil, trace.BadParameter("HMAC key must not be empty")
  	}
  	return &hmacAnonymizer{
  		key: key,
  	}, nil
  }
docs: // NewHMACAnonymizer returns a new HMAC-based anonymizer