[SYNC]

lib/src/sheet/src/models/sheet_store.model.dart

@@ -17,11 +17,16 @@ class SheetStore extends ChangeNotifier {
   }
 
   /// Updates [item] in the store.
-  void update(String itemID, dynamic value) {
+  void update(String itemID, dynamic value, {bool addIfAbsent = false}) {
     if (!_items.containsKey(itemID)) {
-      throw Exception('No item with the ID $itemID exist in the SheetStore, Are you sure you added it?');
+      if (addIfAbsent) {
+        add(itemID, value);
+      } else {
+        throw Exception('No item with the ID $itemID exist in the SheetStore, Are you sure you added it?');
+      }
+    } else {
+      _items[itemID] = value;
     }
-    _items[itemID] = value;
     // This call tells the widgets that are listening to this store to rebuild.
     notifyListeners();
   }