Doctrine custom walker

MyCoolRepository.php

<?php

namespace Application\Infrastructure\Repository;

use Application\Domain\Model\TransactionStatus;
use Application\Infrastructure\Component\DoctrineExtensions\Query\SortableNullsWalker;
use Doctrine\ORM\EntityRepository;
use Doctrine\ORM\Query;

/**
 * MyCool Repository
 * 
 * @package Application\Infrastructure\Repository
 */
class MyCoolRepository extends EntityRepository
{
    /**
     * @param \DateTime $datePayAttemptInterval
     * @return array<MyEntity>
     */
    public function myAmazingGetData(\DateTime $datePayAttemptInterval): array
    {
        $queryBuilder = $this->createQueryBuilder('t');

        $query = $queryBuilder
            ->where(
                $queryBuilder
                    ->expr()
                    ->andX(
                        $queryBuilder
                            ->expr()
                            ->eq('t.status.status', ':status')
                        ,
                        $queryBuilder
                            ->expr()
                            ->orX(
                                $queryBuilder
                                    ->expr()
                                    ->isNull('t.lastDatePayAttempt')
                                ,
                                $queryBuilder
                                    ->expr()
                                    ->lt('t.lastDatePayAttempt', ':datePayAttemptInterval')
                            )
                    )
            )
            ->setParameter('status', TransactionStatus::CONCILIATED)
            ->setParameter('datePayAttemptInterval', $datePayAttemptInterval->format('Y-m-d H:i:s'))
            ->orderBy('t.lastDatePayAttempt', 'ASC')
            ->getQuery()
        ;

        $query->setHint(
            Query::HINT_CUSTOM_OUTPUT_WALKER,
            SortableNullsWalker::class
        );

        $query->setHint(
            "sortableNulls.fields",
            [
                "t.lastDatePayAttempt" => SortableNullsWalker::NULLS_LAST,
            ]
        );

        return $query->getResult();
    }
}

SortableNullsWalker.php

<?php

namespace Application\Infrastructure\Component\DoctrineExtensions\Query;

use Doctrine\ORM\Query\AST\PathExpression;
use Doctrine\ORM\Query\SqlWalker;

/**
 * SortableNullsWalker
 *
 * @package Application\Infrastructure\Component\DoctrineExtensions\Query
 */
class SortableNullsWalker extends SqlWalker
{
    /**
     * Null order types
     */
    const NULLS_FIRST = 'NULLS_FIRST';
    const NULLS_LAST  = 'NULLS_LAST';

    /**
     * {@inheritdoc}
     * @throws \Doctrine\ORM\Query\QueryException
     */
    public function walkOrderByItem($orderByItem)
    {
        $sql = parent::walkOrderByItem($orderByItem);
        $hint = $this
            ->getQuery()
            ->getHint('sortableNulls.fields')
        ;
        $expr = $orderByItem->expression;

        if (is_array($hint) && count($hint)) {
            if ($expr instanceof PathExpression &&
                $expr->type == PathExpression::TYPE_STATE_FIELD
            ) {
                $fieldName = $expr->field;
                $index  = $expr->identificationVariable . '.' . $fieldName;

                $sqlParts = [];
                $sqlParts[] = $this->walkPathExpression($expr) . ' ' . self::getSqlPart($hint[$index]);
                if ($sql) {
                    $sqlParts[] = $sql;
                }

                $sql = implode(', ', $sqlParts);
            }
        }

        return $sql;
    }

    /**
     * @param string $order
     * @return string
     */
    public static function getSqlPart(string $order): string
    {
        switch ($order) {
            case self::NULLS_FIRST:
                return 'IS NOT NULL';
                break;
            case self::NULLS_LAST:
                return 'IS NULL';
                break;
            default:
                return '';
                break;
        }
    }
}