diff --git a/IRaCIS.Core.Application/Service/Visit/SubjectVisitService.cs b/IRaCIS.Core.Application/Service/Visit/SubjectVisitService.cs
index 7bc6db093..4ed21a612 100644
--- a/IRaCIS.Core.Application/Service/Visit/SubjectVisitService.cs
+++ b/IRaCIS.Core.Application/Service/Visit/SubjectVisitService.cs
@@ -437,7 +437,7 @@ namespace IRaCIS.Core.Application.Services
         /// <param name="indto"></param>
         /// <returns></returns>
         [HttpPost]
-        public async Task<VisitStudyDTO?> GetKeySeries(GetReadingVisitStudyListIndto indto)
+        public async Task<VisitStudyDTO> GetKeySeries(GetReadingVisitStudyListIndto indto)
         {
             var rowInfoList = await _readingTableAnswerRowInfoRepository.Where(x => x.VisitTaskId == indto.VisitTaskId && x.StudyId != null).OrderBy(x => x.ReadingQuestionTrial.ShowOrder).ThenBy(x => x.RowIndex).Select(x => new StudyInstanceInfo()
             {
@@ -542,7 +542,7 @@ namespace IRaCIS.Core.Application.Services
                 }
             }
 
-            return null;
+            return new VisitStudyDTO() { StudyId= default(Guid) };
         }
 
         /// <summary>
@@ -664,10 +664,7 @@ namespace IRaCIS.Core.Application.Services
                     {
                         studyList.Insert(0, keySeries);
                     }
-                    else 
-                    {
-                        studyList.Insert(0, new VisitStudyDTO() { StudyId= default(Guid) });
-                    }
+