SocialiteProviders\Manager\Helpers\ConfigRetriever::getFromServices PHP Method

    private function getFromServices($key)
    {
        $keyExists = array_key_exists($key, $this->servicesArray);
        // ADDITIONAL value is empty
        if (!$keyExists && $this->isAdditionalConfig($key)) {
            return;
        }
        // REQUIRED value is empty
        if (!$keyExists) {
            throw new MissingConfigException("Missing services entry for {$this->providerName}.{$key}");
        }
        return $this->servicesArray[$key];
    }