fix(study): 解决学生考试记录查询空指针异常

web-app/src/main/java/com/zcloud/edu/command/query/study/StudentExamRecordQueryExe.java

@@ -48,6 +48,9 @@ public class StudentExamRecordQueryExe {
     }
     public SingleResponse<StudentExamRecordCO> executeGetInfoByStudentId(String studentId){
         StudentExamRecordDO studentExamRecordDO = studentExamRecordRepository.getInfoByStudentId(studentId);
+        if(studentExamRecordDO == null){
+            return SingleResponse.of(null);
+        }
         StudentExamRecordCO studentExamRecordCO = new StudentExamRecordCO();
         BeanUtils.copyProperties(studentExamRecordDO, studentExamRecordCO);
         List<StudentExamRecordItemDO> recordList = studentExamRecordItemRepository.listByExamRecordId(studentExamRecordDO.getStudentExamRecordId());