public function serve(string $collection, string $group, ?string $format = null) : string {
        if ( ! isset($this->app['basset'][$collection])) {
            return '<!-- Basset could not find collection: '.$collection.' -->';
        }

        // Get the collection instance from the array of collections. This instance will be used
        // throughout the building process to fetch assets and compare against the stored
        // manfiest of fingerprints.
        $collection = $this->app['basset'][$collection];

        if ($this->runningInProduction() and $this->app['basset.manifest']->has($collection)) {
            if ($this->app['basset.manifest']->get($collection)->hasProductionFingerprint($group)) {
                return $this->serveProductionCollection($collection, $group, $format);
            }
        }

        return $this->serveDevelopmentCollection($collection, $group, $format);
    }