added error handling for invalid urls

lib/pages/collections_list_page.dart

@@ -66,8 +66,9 @@ class _CollectionsListPageState extends State<CollectionsListPage> {
       selectedCollection: selectedCollection,
       onSavePressed: onCollectionSaved,
       onDeletePressed: () {
-        Storage.deleteCollection(selectedCollection);
-        setState(() {});
+        Storage.deleteCollection(
+          selectedCollection,
+        ).whenComplete(() => setState(() {}));
       },
     ),
   );
@@ -79,7 +80,9 @@ class _CollectionsListPageState extends State<CollectionsListPage> {
     addingNewBookmark = provider.currentMapsLinkMetadata != null;
     return Scaffold(
       appBar: AppBar(
-        title: addingNewBookmark ? Text('Choose Collection') : null,
+        title: addingNewBookmark
+            ? Text('Choose Collection')
+            : Text('Collections'),
         actions: [
           if (addingNewBookmark)
             TextButton(
@@ -92,11 +95,15 @@ class _CollectionsListPageState extends State<CollectionsListPage> {
         onPressed: onAddButtonPressed,
         child: Icon(Icons.add),
       ),
-      body: ListView.builder(
-        itemBuilder: (context, index) =>
-            collectionsListItemBuilder(context, collections.elementAt(index)),
-        itemCount: collections.length,
-      ),
+      body: collections.isNotEmpty
+          ? ListView.builder(
+              itemBuilder: (context, index) => collectionsListItemBuilder(
+                context,
+                collections.elementAt(index),
+              ),
+              itemCount: collections.length,
+            )
+          : Center(child: Text('Create your first Collection to get started!')),
     );
   }
 }