[chore] delete many 시 조건을 null 체크로 처리해 항상 예외로 간주하는 문제 수정 (#147)

src/main/java/hyundai/softeer/orange/admin/controller/AdminEventController.java

@@ -115,7 +115,7 @@ public ResponseEntity<Void> deleteEvent(
     })
     public ResponseEntity<List<DeleteEventNotAllowedReasonDto>> deleteEvents(@Valid @RequestBody DeleteEventsDto dto) {
         var result = eventService.deleteEvents(dto.getEventIds());
-        if(result == null) return ResponseEntity.ok().build();
+        if(result.isEmpty()) return ResponseEntity.ok().build();
         return ResponseEntity.badRequest().body(result);
     }