fix bug

themis-backend/src/main/java/com/qmth/themis/backend/api/TEExamController.java

@@ -303,6 +303,7 @@ public class TEExamController {
             teExam.setId(null);
             teExam.setUpdateId(null);
             teExam.setUpdateTime(null);
+            teExam.setShortCode(null);
             TBUser tbUser = (TBUser) ServletUtil.getRequestAccount();
             teExam.setCreateId(tbUser.getId());
             teExam.setCode(code);