protected static function getReader(?string $identifier): ReaderInterface
    {
        if (!isset(static::$identifiers[$identifier])) {
            throw new \RuntimeException('Unknown identifier "' . $identifier . '" for a configuration file.');
        }

        $readerClass = static::$identifiers[$identifier];

        return new $readerClass();
    }
protected static function getReader(?string $identifier): ReaderInterface
    {
        if (!isset(static::$identifiers[$identifier])) {
            throw new \RuntimeException('Unknown identifier "' . $identifier . '" for a configuration file.');
        }

        $readerClass = static::$identifiers[$identifier];

        return new $readerClass();
    }
Returns a reader for the provided $identifier.

@param string|null $identifier

@throws \RuntimeException if the provided $identifier is not valid

@return ReaderInterface