feat(wip): 경매 입찰 기능

hwe/sammo/DTO/AuctionBidItem.php

@@ -3,12 +3,14 @@
 namespace sammo\DTO;
 
 use sammo\DTO\Attr\JsonString;
+use sammo\DTO\Attr\NullIsUndefined;
 use sammo\DTO\Attr\RawName;
 
 class AuctionBidItem extends DTO
 {
   public function __construct(
-    public int $id,
+    #[NullIsUndefined]
+    public ?int $id,
     #[RawName('auction_id')]
     public int $auctionID,
     public ?int $owner,