[Serializer] fix nullable int cannot be serialized

[nikophil]

Q	A
Branch?	5.4
Bug fix?	yes
New feature?	no
Deprecations?	no
License	MIT

Hello,

previous to this PR such XML could be deserialized correctly, setting null in the value:

<?xml version="1.0" encoding="UTF-8"?>
<DummyNullableInt>
	<value/>
</DummyNullableInt>

class DummyNullableInt
{
    public function __construct(
        public int|null $value = null
    )
    {}
}

but now it creates the following error:

Uninitialized string offset 0

/home/nikophil/works/symfony/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php:495
/home/nikophil/works/symfony/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php:630
/home/nikophil/works/symfony/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php:377
/home/nikophil/works/symfony/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php:246
/home/nikophil/works/symfony/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php:346

I looked for any issue or PR mentioning this problem, but couldn't find it. So here is a fix

ping @Jeroeny

[carsonbot]

Hey!

Thanks for your PR. You are targeting branch "7.1" but it seems your PR description refers to branch "6.4".
Could you update the PR description or change target branch? This helps core maintainers a lot.

Cheers!

Carsonbot

[nicolas-grekas]

that's for 5.4 I suppose?
can you please rebase + retarget?

[nikophil]

@nicolas-grekas done

the problem only occurs with nullable types properties, hence the @requires PHP 8 tag

[nicolas-grekas]

Thank you @nikophil.