Typed Property Defaults: problem with nullable properties

Hi,

Since the 2.9.2 release, my nullable php typed properties are not correctly taken into account by Doctrine.
For example, this attribute is not nullable in database:

``` php
 #[ORM\Column]
 public ?\DateTimeImmutable $canceledAt = null;
```

I needed to downgrade to 2.9.1.

Thx