Minor change to how Lit 3.0 will work.

PropertyValues.get can return undefined or null.

Release-Notes: skip
Change-Id: I82235bb0f7a90f464910e824a4e548fcd81b6b31

polygerrit-ui/app/elements/admin/gr-permission/gr-permission.ts

diff --git a/polygerrit-ui/app/elements/admin/gr-permission/gr-permission.ts b/polygerrit-ui/app/elements/admin/gr-permission/gr-permission.ts
index 7f03d1d..ff7a528 100644
--- a/polygerrit-ui/app/elements/admin/gr-permission/gr-permission.ts
+++ b/polygerrit-ui/app/elements/admin/gr-permission/gr-permission.ts
@@ -127,8 +127,9 @@
   }
 
   override willUpdate(changedProperties: PropertyValues<GrPermission>): void {
-    if (changedProperties.has('editing')) {
-      this.handleEditingChanged(changedProperties.get('editing'));
+    const oldEditing = changedProperties.get('editing');
+    if (oldEditing !== null && oldEditing !== undefined) {
+      this.handleEditingChanged(oldEditing);
     }
     if (
       changedProperties.has('permission') ||