Fix TardinessField.vue errors

aleksis/apps/alsijil/frontend/components/coursebook/absences/TardinessField.vue

@@ -81,6 +81,10 @@ export default {
       this.saveValue(this.previousValue);
     },
     processValueObjectOptional(value) {
+      if (value === null || value === undefined) {
+        return 0;
+      }
+
       if (Object.hasOwn(value, "value")) {
         return value.value;
       }
@@ -159,7 +163,7 @@ export default {
           {{
             $t("alsijil.personal_notes.confirm_delete_tardiness", {
               tardiness: previousValue,
-              name: participations.map((p) => p.person.firstName).join(", "),
+              name: participations.map((p) => p.person?.firstName).join(", "),
             })
           }}
         </template>