code: func ConvertUsernamesToIdentifiers(usernames []string, valMgr *validation.Manager) ([]string, error) {
  	identifiers := []string{}
  	checkedUsers := map[string]bool{}
  	for _, u := range usernames {
  		checkedUsers[u] = false
  	}
  	emails, err := valMgr.GetValidatedEmailAddressesByUsernames(usernames)
  	if err != nil {
  		return identifiers, err
  	}
  	for _, validatedEmail := range emails {
  		if !checkedUsers[validatedEmail.Username] {
  			identifiers = append(identifiers, validatedEmail.EmailAddress)
  			checkedUsers[validatedEmail.Username] = true
  		}
  	}
  	checkPhoneUsernames := []string{}
  	for username, checked := range checkedUsers {
  		if !checked {
  			checkPhoneUsernames = append(checkPhoneUsernames, username)
  		}
  	}
  	validatedPhoneNumbers, err := valMgr.GetValidatedPhoneNumbersByUsernames(checkPhoneUsernames)
  	if err != nil {
  		return identifiers, err
  	}
  	for _, validatedPhone := range validatedPhoneNumbers {
  		if !checkedUsers[validatedPhone.Username] {
  			identifiers = append(identifiers, validatedPhone.Phonenumber)
  			checkedUsers[validatedPhone.Username] = true
  		}
  	}
  	return identifiers, nil
  }
docs: // ConvertUsernamesToIdentifiers converts a list of usernames to a list of user identifiers