diff --git a/superset-frontend/src/features/alerts/AlertReportModal.tsx b/superset-frontend/src/features/alerts/AlertReportModal.tsx
index c297da2d71db..deb49b4d45ed 100644
--- a/superset-frontend/src/features/alerts/AlertReportModal.tsx
+++ b/superset-frontend/src/features/alerts/AlertReportModal.tsx
@@ -885,7 +885,7 @@ const AlertReportModal: FunctionComponent<AlertReportModalProps> = ({
 
     // Need to make sure grace period is not lower than TIMEOUT_MIN
     if (value === 0) {
-      updateAlertState(target.name, null);
+      updateAlertState(target.name, undefined);
     } else {
       updateAlertState(
         target.name,