getValue method
Gets the value from SharedPreferences.
If the value doesn't exist and defaultValue is provided, stores the default value and returns it.
Implementation
Future<T?> getValue(SharedPreferencesAsync prefs) async {
final exists = await _exists(prefs);
if (!exists && defaultValue != null) {
await setValue(prefs, defaultValue as T);
return defaultValue;
}
return await adapter.getter(prefs, key);
}