Symfony version(s) affected

6.3.0

Description

RequestPayloadValueResolver always returns null when mapping query strings and query string is empty.

This is problematic when using a DTO where all arguments have default values, e.g.

class MyDto {
    public function __construct(public string $foo = "bar")
    {}
}

How to reproduce

Controller:

class MyDto {
    public function __construct(public string $foo = "bar")
    {}
}

class FooController extends AbstractController
{
    #[Route("/foo", name: "foo", methods: ["GET"])]
    public function getPaginated(
        #[MapQueryString] MyDto $myDto,
    ): JsonResponse
    {
        return $this->json($myDto);
    }
}

GET /foo -> 404 HttpException
GET /foo?foo=baz -> 200 {"foo": "baz"}

Possible Solution

Remove this early return and let the serializer decide what to do with an empty query string.

Additional Context

No response