调整字段空属性

src/Hotline/Exams/ExamManages/UserExam.cs

@@ -72,6 +72,6 @@ namespace Exam.ExamManages
         /// </summary>
         [SugarColumn(ColumnDescription = "是否补考")]
         [Description("是否补考")]
-        public bool IsReExam { get; set; }
+        public bool? IsReExam { get; set; }
     }
 }