public function formattedCredentials(string $relationship, string $formatter)
    {
        if (empty($this->credentialFormatters[$formatter])) {
            throw new NoCredentialFormatterFoundException(sprintf('There is no credential formatter named "%s" registered. Did you remember to call registerFormatter()?', $formatter));
        }

        return $this->credentialFormatters[$formatter]($this->credentials($relationship));
    }