upgrade & fix jpa.

examcloud-core-questions-dao/src/main/java/cn/com/qmth/examcloud/core/questions/dao/PaperDetailUnitRepo.java

@@ -12,6 +12,7 @@ import cn.com.qmth.examcloud.core.questions.dao.entity.PaperDetailUnit;
 import cn.com.qmth.examcloud.core.questions.dao.entity.Question;
 
 import java.util.List;
+import java.util.Optional;
 
 
 public interface PaperDetailUnitRepo extends MongoRepository<PaperDetailUnit, String>,QueryByExampleExecutor<PaperDetailUnit> {
@@ -22,7 +23,7 @@ public interface PaperDetailUnitRepo extends MongoRepository<PaperDetailUnit, St
     List<PaperDetailUnit> findByPaperIdOrderByNumber(String paperId);
     List<PaperDetailUnit> findByQuestion(Question question);
     List<PaperDetailUnit> findByQuestionIn(List<Question> questionList);
-    PaperDetailUnit findById(String id);
+    Optional<PaperDetailUnit> findById(String id);
     List<PaperDetailUnit> findByQuestionType(QuesStructType quesType);
     Long countByPaperDetail(PaperDetail paperDetail);
     /**