fix

zhongzheng-system/src/main/java/com/zhongzheng/modules/grade/service/impl/ClassGradeUserServiceImpl.java

@@ -1954,7 +1954,7 @@ public class ClassGradeUserServiceImpl extends ServiceImpl<ClassGradeUserMapper,
                     if(photoList.size()>0){
                         classPeriodVo.setStudyStartTime(photoList.get(0).getCreateTime());
                     }
-                    if(startTotalTime==0L||startTotalTime.longValue()>classPeriodVo.getStudyStartTime().longValue()){
+                    if((Validator.isNotEmpty(classPeriodVo.getStudyStartTime())&&startTotalTime==0L)||(Validator.isNotEmpty(classPeriodVo.getStudyStartTime())&&startTotalTime.longValue()>classPeriodVo.getStudyStartTime().longValue())){
                         startTotalTime = classPeriodVo.getStudyStartTime();
                     }
                     if(endTotalTime==0L||(Validator.isNotEmpty(classPeriodVo.getStudyEndTime())&&endTotalTime.longValue()<classPeriodVo.getStudyEndTime().longValue())){