private function discoverCustomFields()
    {
        $path = $this->rootDir.'/'.$this->directory;
        $finder = new Finder();
        $finder->files()->in($path);

        /** @var SplFileInfo $file */
        foreach ($finder as $file) {
            $class = $this->classForFile($file);
            /* @var \Lullabot\Mpx\DataService\Annotation\CustomField $annotation */
            $this->registerAnnotation($class);
        }
    }