Merge pull request #37 from Nexters/refactor/use-findById

[REFACTOR] findById 적용 및 NOTFOUND 핸들링 구현 (#36)

src/main/java/com/nextroom/oescape/service/HintService.java

@@ -60,7 +60,7 @@ public List<HintDto.HintListResponse> getHintList(Long themeId) {
     }
 
     public Object getHintListByThemeId(Long themeId) {
-        Theme theme = themeRepository.getReferenceById(themeId);
+        Theme theme = themeRepository.findById(themeId).orElseThrow(() -> new CustomException(TARGET_THEME_NOT_FOUND));
 
         return theme.getHints().stream().map(Hint::toHintListResponse).toList();
     }