fix: bug in the content type parser of fastify

src/modules/subscriptions/entities/subscription.entity.ts

@@ -32,7 +32,7 @@ export class SubscriptionPlan extends BaseEntity {
   userSubscriptions: UserSubscription[];
 
   @ManyToOne(() => Discount, (discount) => discount.subscriptionPlans, { nullable: true, onUpdate: "CASCADE" })
-  directDiscount?: Discount;
+  directDiscount: Discount | null;
 
   @DeleteDateColumn({ nullable: true })
   deletedAt?: Date;