TYPO3 Core

I've just analyzed the provided CategoriesValuesMapper and found the problem there. URL that cannot be resolved need to return null, in that mapper example, the return value is always a string (which might be empty).

   public function resolve(string $value): ?string
    {
        //DebuggerUtility::var_dump($value, 'resolve');
        $categorieIDsArray = explode('_',$value);
        $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('sys_category');
        $categories = $queryBuilder->select('uid', 'slug')
            ->from('sys_category')
            ->where(
                $queryBuilder->expr()->in('slug', $queryBuilder->createNamedParameter($categorieIDsArray, Connection::PARAM_STR_ARRAY)),
            )
            ->orderBy('parent')
            ->execute()
            ->fetchAll();
        $routing = strval($categories[0]['uid']);
### -> ###         ^^ that's the problem, `$routing` is always as string
        if($categories[1]) {
            $routing .= "," . strval($categories[1]['uid']);
        }

        if (isset($routing)) {
            return (string)$routing;
        }
        return null;
    }

Potential modification to return null when having mismatches (and have 404 handling working):

   public function resolve(string $value): ?string
    {
        //DebuggerUtility::var_dump($value, 'resolve');
        $categorieIDsArray = explode('_',$value);
        $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('sys_category');
        $categories = $queryBuilder
            /* ... */
            ->fetchAll();

        // no category could be resolved, return `null`, triggers 404 handling
        if (!isset($categories[0]['uid'])) {
            return null;
        }

        $routing = $categories[0]['uid'];
        if (isset($categories[1]['uid])) {
            $routing .= "," . strval($categories[1]['uid']);
        }

        return $routing;
    }

Thank you, it was my fault.