[10.x] fix Validator::validated get nullable array

[helitik]

Since laravel >= 9.x, Illuminate\Validation\Validator::validated no longer allows to retrieve a nullable|array validation rule with a nested key.

To reproduce:

use Illuminate\Support\Facades\Validator;

$validator = Validator::make(
    [
        'x' => null,
    ],
    [
        'x' => ['array', 'nullable'],
        'x.key' => ['string'],
    ],
);

dd($validator->validate()); // return [] instead of ["x" => null]

This PR fix Illuminate\Validation\Validator::validated to allowed nullable array.