Null check operator used on a null value in ReorderableAnimatedBuilderState.removeItem.

[Sereen-Kh]

I got this Exception :
reorderable_animated_builder.dart in ReorderableAnimatedBuilderState.removeItem.. at line 628 within animated_reorderable_list

Null check operator used on a null value

[centy]

I have same crash,

Fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: Null check operator used on a null value
at AnimationController.stop(animation_controller.dart:903)
at AnimationController._animateToInternal(animation_controller.dart:673)
at AnimationController.forward(animation_controller.dart:484)
at ReorderableAnimatedBuilderState.insertItem.(reorderable_animated_builder.dart:571)

AI analyze:
Crash summary

• Stack trace shows AnimationController.stop blowing up because _ticker is null, meaning AnimationController.forward() is being invoked on a controller that has already been disposed.

• The only place where we trigger animated insert/remove logic is AnimatedListView inside QuestList (lib/feature/quest/ui/quest_dialog.dart), which comes from the animated_reorderable_list package. It diffs items and calls insertItem/removeItem automatically whenever the cubit emits an updated quest list.@lib/feature/quest/ui/quest_dialog.dart#171-255

• Looking at the package source (animated_reorderable_list/lib/src/builder/reorderable_animated_builder.dart), insertItem starts an animation by awaiting sizeController.forward() and then calling controller.forward() on the same _ActiveItem. When the widget is disposed (e.g., because the Quest dialog closes) before that second forward() runs, the controllers are disposed in dispose(), so the next forward() call hits the null ticker and Crashlytics reports “Null check operator used on a null value.”@animated_reorderable_list/lib/src/builder/reorderable_animated_builder.dart#503-575 @animated_reorderable_list/lib/src/builder/reorderable_animated_builder.dart#430-472

**Why it happens in **

1. Quest data refreshes frequently (QuestCubit.refresh() emits whenever quests change).@lib/feature/quest/bloc/quest_cubit.dart#25-60
2. Closing the Quest dialog (or otherwise removing QuestList) disposes the underlying AnimatedListView while animations are still running.
3. The package bug described above fires during the tail end of an insert animation, so any quest refresh that happens right as the dialog is closing can trigger the crash

Solution

Patch the dependency
Modify ReorderableAnimatedBuilderState.insertItem checks if (!mounted) return; before continuing the chained animation, and skips controller.forward() if controller.isDisposed or sizeController.isDismissed. The same guard should be added in removeItem as well.