ImplementedReturnTypeMismatch since version 3.4.6 when using Doctrine

[leroy0211]

Since version 3.4.6 psalm throws an error ImplementedReturnTypeMismatch when using Doctrine. The error occurs on the find method of any Doctrine Repository.

The exact error is:
For privacy reasons the Repository is renamed to Foo.

ERROR: ImplementedReturnTypeMismatch - src/Repository/FooRepository.php:9:12 - The return type 'null|T as mixed' for Doctrine\Common\Persistence\ObjectRepository::find is different to the implemented return type for Doctrine\ORM\EntityRepository::find 'null|App\Entity\Foo'

I've validated if it's happening since this version by fixing the version to 3.4.5 and this error doesn't occur. When going to version 3.4.6 or any version higher, the error occurs.

The repository is just a simple repository generated from the maker-bundle command. But for any reference, here it is:

<?php

namespace App\Repository;

use App\Entity\Foo;
use Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository;
use Symfony\Bridge\Doctrine\RegistryInterface;

/**
 * @method Foo|null find($id, $lockMode = null, $lockVersion = null)
 * @method Foo|null findOneBy(array $criteria, array $orderBy = null)
 * @method Foo[]    findAll()
 * @method Foo[]    findBy(array $criteria, array $orderBy = null, $limit = null, $offset = null)
 */
class FooRepository extends ServiceEntityRepository
{
    public function __construct(RegistryInterface $registry)
    {
        parent::__construct($registry, Foo::class);
    }
}

The error occurs on the line:

 * @method Foo|null find($id, $lockMode = null, $lockVersion = null)

[muglug]

Reproduced in a test here: 7d05568#diff-463cd1d277819cf78d66dadc84404891R930

cc @weirdan, as it involves your plugin (but you did nothing wrong). You may also want to stub out Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository with something like

/**
 * @template T
 * @template-extends EntityRepository<T>
 */
class ServiceEntityRepository extends EntityRepository {
}

to allow people to use @template-extends<Foo> in their repo files