fix: 마지막으로 보낸 알림이 없을 때, 모임 생성일 반

Author: JunRain2

tuk-api/src/main/kotlin/nexters/tuk/application/gathering/GatheringMemberService.kt

@@ -6,7 +6,6 @@ import nexters.tuk.contract.ErrorType
 import nexters.tuk.domain.gathering.*
 import org.springframework.stereotype.Service
 import org.springframework.transaction.annotation.Transactional
-import java.time.LocalDateTime
 
 @Service
 class GatheringMemberService(
@@ -39,7 +38,8 @@ class GatheringMemberService(
                 GatheringMemberResponse.MemberGatherings(
                     id = memberGathering.gathering.id,
                     name = memberGathering.gathering.name,
-                    lastPushedAt = memberGathering.gathering.lastPushedAt ?: LocalDateTime.now(),
+                    lastPushedAt = memberGathering.gathering.lastPushedAt
+                        ?: memberGathering.gathering.createdAt,
                 )
             }.sortedBy { it.name }
     }