Nullable arrays of BackedEnums or Objects are not properly deserialized

[MariusJam]

API Platform version(s) affected: ^4.2

Description
When using Symfony 7.1+ and API Platform 4.2+, properties defined as nullable arrays/collections of BackedEnums or Objects fail to be properly deserialized during POST or PATCH requests. Instead of being denormalized into instances of the Enum/Entity, the elements are left as raw strings.

This eventually results in database-level errors:
Doctrine\ORM\Mapping\ReflectionEnumProperty::getValue(): Argument #1 ($item) must be of type BackedEnum, string given

The bug is caused by API Platform's AbstractItemNormalizer::createAndValidateAttributeValue which checks if a property's type is a collection of objects using:

if (
    ($t instanceof CollectionType && $collectionValueType instanceof ObjectType)
    || ($t instanceof LegacyType && $t->isCollection() && null !== $collectionValueType && null !== $collectionValueType->getClassName())
)

When a property is nullable, Symfony's TypeInfo extracts a NullableType for its collection values. Since NullableType wraps the actual ObjectType/BackedEnumType but does not directly inherit from ObjectType, the condition $collectionValueType instanceof ObjectType evaluates to false. As a result, API Platform fails to delegate the collection items' denormalization to the Serializer.

How to reproduce

1. Define a BackedEnum:

namespace App\Enum;

enum ContactNotificationsEnum: string
{
    case Email = 'email';
    case Sms = 'sms';
}

2. Define a Doctrine entity with a nullable, array of BackedEnums column using Doctrine's SIMPLE_ARRAY (or any typed array PHP property):

namespace App\Entity;

use ApiPlatform\Metadata\ApiResource;
use App\Enum\ContactNotificationsEnum;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\DBAL\Types\Types;

#[ORM\Entity]
#[ApiResource]
class CompanyContact
{
    #[ORM\Id]
    #[ORM\GeneratedValue]
    #[ORM\Column]
    public ?int $id = null;

    /**
     * @var ContactNotificationsEnum[] $notificationType
     */
    #[ORM\Column(type: Types::SIMPLE_ARRAY, enumType: ContactNotificationsEnum::class, nullable: true)]
    public array $notificationType = [];
}

3. Send a POST request to create a new CompanyContact:

{
  "notificationType": ["email"]
}

Results:

A HTTP 500 error is thrown by Doctrine:
Doctrine\ORM\Mapping\ReflectionEnumProperty::getValue(): Argument #1 ($item) must be of type BackedEnum, string given because the array elements remained raw strings.

Additional Context

I guess this behavior only started happening after the transition to Symfony's TypeInfo.

[soyuka]

Thanks for the report!