protected function getReferenceSource(Model $model, $source = null)
    {
        if (null === $source) {
            // Get model information for the model
            $information = $this->getInformationRepository()->getByModel($model);

            if ($information && $information->reference->source) {
                $source = $information->reference->source;
            }
        }

        if ( ! $source) return null;

        return $source;
    }