diff --git a/Tiobon.Core.Common/Helper/ExamHelper.cs b/Tiobon.Core.Common/Helper/ExamHelper.cs
index 9a68ad04..a6ffb480 100644
--- a/Tiobon.Core.Common/Helper/ExamHelper.cs
+++ b/Tiobon.Core.Common/Helper/ExamHelper.cs
@@ -59,9 +59,10 @@ public class ExamHelper
                         var content = recordAnswers.Where(x => x.ExamRecordDetailId == detail.Id).First().AnswerContent;
                         var count1 = completionAnswers1.Count;
 
-                        for (int i = 0; i < completionAnswers1.Count; i++)
-                            if (content.IndexOf(completionAnswers1[i].AnswerContent) > -1)
-                                count1--;
+                        if (!content.IsNull())
+                            for (int i = 0; i < completionAnswers1.Count; i++)
+                                if (content.IndexOf(completionAnswers1[i].AnswerContent) > -1)
+                                    count1--;
 
                         if (count1 == 0)
                         {