defaultItems method
Provides the default list of items to display when items is null.
Subclasses must implement this method to define fallback behavior. For example, pickers might return all available countries, currencies, or languages from a global list, or use translation cache keys from theme or locale delegate.
The context parameter allows subclasses to access theme data or
localization delegates to determine appropriate default items.
Implementation
@override // coverage:ignore-line
Iterable<T> defaultItems(BuildContext? context) => const [];