resolves #486

package/lib/src/beamer.dart

@@ -57,7 +57,7 @@ class Beamer extends StatefulWidget {
 /// A [State] for [Beamer].
 class BeamerState extends State<Beamer> {
  /// A parent Router of this Beamer / Router.
- late Router parent;
+ late Router? parent;
 
  /// A getter for [BeamerDelegate] of the [Beamer] whose state is this.
  BeamerDelegate get routerDelegate => widget.routerDelegate;
@@ -69,17 +69,26 @@ class BeamerState extends State<Beamer> {
  void didChangeDependencies() {
  super.didChangeDependencies();
  parent = Router.of(context);
- routerDelegate.parent = parent.routerDelegate as BeamerDelegate;
+ routerDelegate.parent = parent!.routerDelegate as BeamerDelegate;
+ }
+
+ @override
+ void dispose() {
+ parent = null; 
+ routerDelegate.parent = null;
+ super.dispose();
  }
 
  @override
  Widget build(BuildContext context) {
+ // The parent will only be null, if this state is disposed and therefore 
+ // `build` cannot be called on it any more.
  final backButtonDispatcher = widget.backButtonDispatcher ??
- ((parent.backButtonDispatcher is BeamerBackButtonDispatcher &&
+ ((parent!.backButtonDispatcher is BeamerBackButtonDispatcher &&
  widget.createBackButtonDispatcher)
  ? BeamerChildBackButtonDispatcher(
  parent:
- parent.backButtonDispatcher! as BeamerBackButtonDispatcher,
+ parent!.backButtonDispatcher! as BeamerBackButtonDispatcher,
  delegate: routerDelegate,
  )
  : null);

package/lib/src/beamer_delegate.dart

@@ -74,7 +74,13 @@ class BeamerDelegate extends RouterDelegate<RouteInformation>
  /// `*App.router` and at least one more [Beamer] in the Widget tree.
  BeamerDelegate? get parent => _parent;
  set parent(BeamerDelegate? parent) {
- if (parent == null || _parent == parent) {
+ if(parent == null && _parent != null) {
+ _parent!.removeListener(_updateFromParent);
+ _parent!._children.remove(this);
+ _parent = null;
+ return;
+ }
+ if (_parent == parent) {
  return;
  }
  _parent = parent;
@@ -398,7 +404,7 @@ class BeamerDelegate extends RouterDelegate<RouteInformation>
 
  // run guards on _beamLocationCandidate
  final context = _context;
- if (context != null && context is Element && (context as Element).dirty == false) { 
+ if (context != null) {
  final didApply = _runGuards(context, _beamLocationCandidate);
  _didRunGuards = true;
  if (didApply) {