PUT or PATCH with null values doesn't clear the value of nullable ManyToOne property of ORM entity

[VictorKrasnov]

API Platform version(s) affected: 3.3.2

Description
If you have some ORM entity with ManyToOne relation, no way to clear this relations. Or I can't find this possibility.

How to reproduce

1. Add entity like this:

   #[ORM\Entity(repositoryClass: OrderRepository::class)]
   #[ORM\Table('orders')]
   class Order
   {
   # ..... other properties is here
   
   #[ORM\ManyToOne(targetEntity: ...)]
   #[ORM\JoinColumn(nullable: true)]
   #[Groups(...)]
   protected ?TradingContractInterface $tradingContract = null;
   
   public function getTradingContract(): ?TradingContractInterface
   {
       return $this->tradingContract;
   }
   
   public function setTradingContract(?TradingContractInterface $tradingContract = null): static
   {
       $this->tradingContract = $tradingContract;
       return $this;
   }
   }

2. Publish REST methods with API Platform (in my case I did it with yaml):

   
   resources:
   App\Order:
   shortName: Order
   description: Order entity.
   operations:
     - class: ApiPlatform\Metadata\GetCollection
       uriTemplate: /orders
       normalizationContext: { groups: ['order:list', 'reference'] }
       createdAt:
         createdAt: 'DESC'
       paginationItemsPerPage: 20
     - class: ApiPlatform\Metadata\Get
       uriTemplate: /orders/{id}
       normalizationContext: { groups: ['order:read', 'reference'] }
     - class: ApiPlatform\Metadata\Post
       uriTemplate: /orders
       normalizationContext: { groups: ['order:read', 'reference'] }
       denormalizationContext: { groups: ['order:create'] }
       processor: Ecomla\SalesBundle\ApiPlatform\State\Order\OrderCreateProcessor
     - class: ApiPlatform\Metadata\Patch
       uriTemplate: /admin/orders/{id}
       normalizationContext: { groups: ['order:read', 'reference'] }
       denormalizationContext: { groups: ['order:update', 'reference'] }
       processor: Ecomla\SalesBundle\ApiPlatform\State\Order\OrderUpdateProcessor
     - class: ApiPlatform\Metadata\Put
       uriTemplate: /admin/orders/{id}
       normalizationContext: { groups: ['order:read', 'reference'] }
       denormalizationContext: { groups: ['order:update', 'reference'] }
       processor: Ecomla\SalesBundle\ApiPlatform\State\Order\OrderUpdateProcessor
     - class: ApiPlatform\Metadata\Delete
       uriTemplate: /admin/orders/{id}
       normalizationContext: { groups: ['order:read', 'reference'] }
   routePrefix: ....

3. Try to update entity with PATCH or PUT /admin/orders/{id} with json like:
```json
{
   # ...other properties
   tradingContract: null
}

Expected behaviour: PATCH and PUT methods should clear current value of property tradingContract end return json without tradingContract property (due to skip_null_values option with value true passed to normaliser).

Actual behaviour: Property did not set to null, and the response includes property tradingContract with old data.

Possible Solution
I think you should change current logic of default denormaliser or add some config options to switch this behaviour.

[soyuka]

Can't you set skip_null_values to false in the denormalizer context? Maybe that it should be the default during denormalization (@dunglas)