fix bug

src/modules/examwork/view/offlineExam.vue

@@ -277,7 +277,7 @@ export default {
         duration: 120,
         enable: "true",
         specialSettingsEnabled: false,
-        specialSettingsType: "",
+        specialSettingsType: null,
         properties: {
           CAN_UPLOAD_ATTACHMENT: "true",
           OFFLINE_UPLOAD_FILE_TYPE: "",
@@ -401,4 +401,4 @@ export default {
 .input >>> .el-input__inner {
   -webkit-appearance: button;
 }
-</style>
+</style>