public function map(array $parts): array
    {
        if (count($parts) < 2) {
            return [$this->handleSinglePart($parts[0])];
        }

        $pos = $this->findFirstnamePosition($parts);

        if (null !== $pos) {
            $parts[$pos] = new Firstname($parts[$pos]);
        }

        return $parts;
    }