must have one button type selected

interface/src/app/main/SchedulerDialog.tsx

@@ -164,6 +164,7 @@ const SchedulerDialog = ({
           exclusive
           disabled={!creating}
           onChange={(_event, flag: ScheduleFlag) => {
+            if (flag !== null) {
               setFieldErrors(undefined); // clear any validation errors
               setScheduleType(flag);
               // wipe the time field when changing the schedule type
@@ -179,6 +180,7 @@ const SchedulerDialog = ({
                   ? { ...editItem, flags: 0 }
                   : { ...editItem, flags: flag }
               );
+            }
           }}
         >
           <ToggleButton value={ScheduleFlag.SCHEDULE_DAY}>