protected function getFilePath($metaType, $key)
    {
        $method = $this->getFindMethod($metaType);
        $path = $this->fileLocator->$method($key, $this->getExtension());
        if (null === $path) {
            throw MetadataException::fatalDriverError($key, sprintf('No mapping file was found.', $path));
        }
        return $path;
    }