refactor: 회원의 예약 상세 조회시 결제 정보를 nullable로 수정

src/main/kotlin/roomescape/payment/web/PaymentDTO.kt

@@ -34,12 +34,12 @@ data class PaymentRetrieveResponse(
     val status: PaymentStatus,
     val requestedAt: OffsetDateTime,
     val approvedAt: OffsetDateTime,
-    val detail: PaymentDetailResponse,
+    val detail: PaymentDetailResponse?,
     val cancel: PaymentCancelDetailResponse?,
 )
 
 fun PaymentEntity.toRetrieveResponse(
-    detail: PaymentDetailResponse,
+    detail: PaymentDetailResponse?,
     cancel: PaymentCancelDetailResponse?
 ): PaymentRetrieveResponse {
     return PaymentRetrieveResponse(

src/main/kotlin/roomescape/reservation/business/ReservationService.kt

@@ -118,7 +118,7 @@ class ReservationService(
 
         val reservation: ReservationEntity = findOrThrow(id)
         val user: UserContactRetrieveResponse = userService.findContactById(reservation.userId)
-        val paymentDetail: PaymentRetrieveResponse = paymentService.findDetailByReservationId(id)
+        val paymentDetail: PaymentRetrieveResponse? = paymentService.findDetailByReservationId(id)
 
         return reservation.toReservationDetailRetrieveResponse(
             user = user,

src/main/kotlin/roomescape/reservation/web/ReservationDto.kt

@@ -50,12 +50,12 @@ data class ReservationDetailRetrieveResponse(
     val id: Long,
     val user: UserContactRetrieveResponse,
     val applicationDateTime: LocalDateTime,
-    val payment: PaymentRetrieveResponse,
+    val payment: PaymentRetrieveResponse?,
 )
 
 fun ReservationEntity.toReservationDetailRetrieveResponse(
     user: UserContactRetrieveResponse,
-    payment: PaymentRetrieveResponse,
+    payment: PaymentRetrieveResponse?,
 ): ReservationDetailRetrieveResponse {
     return ReservationDetailRetrieveResponse(
         id = this.id,