reviseAugmentItems method
Adds all the items that are not already present, but does not replace existing items.
Implementation
TSubclass reviseAugmentItems(Iterable<TModel> newItems) {
final revised = Map<String, TModel>.from(items);
for(final item in newItems) {
final id = itemId(item);
if(!revised.containsKey(id)) {
revised[id] = item;
}
}
return reviseItems(revised);
}