public function setCredentialsName($credentialsName = null)
    {
        // No credentials name.
        if (is_null($credentialsName)) {
            $credentialsName = config('personality-insights.default_credentials');
        }

        // Credentials does not exist.
        if (! config()->has('personality-insights.credentials.'.$credentialsName)) {
            throw new InvalidCredentialsName;
        }

        $this->credentialsName = $credentialsName;

        return $this;
    }