diff --git a/IRaCIS.Core.Application/Service/Reading/Dto/ReadingImageTaskViewModel.cs b/IRaCIS.Core.Application/Service/Reading/Dto/ReadingImageTaskViewModel.cs
index 3579fd2ba..e682396e3 100644
--- a/IRaCIS.Core.Application/Service/Reading/Dto/ReadingImageTaskViewModel.cs
+++ b/IRaCIS.Core.Application/Service/Reading/Dto/ReadingImageTaskViewModel.cs
@@ -680,7 +680,7 @@ namespace IRaCIS.Core.Application.Service.Reading.Dto
 
         public bool UpdateMark { get; set; } = false;
 
-        public string param { get; set; }
+        public string param { get; set; } = string.Empty;
 
         public List<ChangeDicomReadingQuestionAnswerDto> Answers { get; set; }