diff --git a/public/js/components/ClassSchedule/ClassScheduleCalendarSelector.js b/public/js/components/ClassSchedule/ClassScheduleCalendarSelector.js
index 7ab62d758..54c06a86b 100644
--- a/public/js/components/ClassSchedule/ClassScheduleCalendarSelector.js
+++ b/public/js/components/ClassSchedule/ClassScheduleCalendarSelector.js
@@ -1079,7 +1079,7 @@ export default {
 
       let dropzoneElementDataNumber =
         this.getElementDataNumber(closestPartBody);
-      if (!dropzoneElementDataNumber) {
+      if (dropzoneElementDataNumber === null || dropzoneElementDataNumber === undefined) {
         return;
       }