Bug 1231434 - Add 'Delete All' context menu entry to storage inspector r=mratcliffe

MozReview-Commit-ID: 4YNXmhtriRS

devtools/client/shared/widgets/TableWidget.js

@@ -803,6 +803,9 @@ TableWidget.prototype = {
     if (typeof item == "string") {
       item = this.items.get(item);
     }
+    if (!item) {
+      return;
+    }
     let removed = this.items.delete(item[this.uniqueId]);
 
     if (!removed) {