Called by the Router when it detects a route information may have changed as a result of rebuild.
If this getter returns non-null, the Router will start to report new route information back to the engine. In web applications, the new route information is used for populating browser history in order to support the forward and the backward buttons.
When overriding this method, the configuration returned by this getter must be able to construct the current app state and build the widget with the same configuration in the build method if it is passed back to the setNewRoutePath. Otherwise, the browser backward and forward buttons will not work properly.
By default, this getter returns null, which prevents the Router from reporting the route information. To opt in, a subclass can override this getter to return the current configuration.
This getter is also used by the Router to implement state restoration. During state serialization, the Router will persist the current configuration and during state restoration pass it back to the delegate by calling setRestoredRoutePath.
T? get currentConfiguration => null;