Unhandled Exception: Null check operator used on a null value

[woyl]

E/flutter ( 1104): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Null check operator used on a null value
E/flutter ( 1104): #0 ScrollPosition.viewportDimension (package:flutter/src/widgets/scroll_position.dart:262:53)
E/flutter ( 1104): #1 _PagePosition.getPixelsFromPage (package:flutter/src/widgets/page_view.dart:387:19)
E/flutter ( 1104): #2 PageController.animateToPage (package:flutter/src/widgets/page_view.dart:200:16)
E/flutter ( 1104): #3 _TransformerPageViewState.onChangeNotifier (package:card_swiper/src/transformer_page_view/transformer_page_view.dart:583:14)
E/flutter ( 1104): #4 ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:403:24)
E/flutter ( 1104): #5 IndexController.next (package:card_swiper/src/transformer_page_view/index_controller.dart:110:5)
E/flutter ( 1104): #6 _SwiperTimerMixin._onTimer (package:card_swiper/src/swiper.dart:391:24)
E/flutter ( 1104): #7 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
E/flutter ( 1104): #8 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
E/flutter ( 1104): #9 _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:189:12)

[Nuyoahhjh]

E/flutter ( 3362): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Null check operator used on a null value
E/flutter ( 3362): #0 ScrollPosition.viewportDimension (package:flutter/src/widgets/scroll_position.dart:260:53)
E/flutter ( 3362): #1 _PagePosition.getPixelsFromPage (package:flutter/src/widgets/page_view.dart:381:19)
E/flutter ( 3362): #2 PageController.animateToPage (package:flutter/src/widgets/page_view.dart:198:16)
E/flutter ( 3362): #3 _TransformerPageViewState.onChangeNotifier (package:card_swiper/src/transformer_page_view/transformer_page_view.dart:583:14)
E/flutter ( 3362): #4 ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:433:24)
E/flutter ( 3362): #5 IndexController.next (package:card_swiper/src/transformer_page_view/index_controller.dart:110:5)
E/flutter ( 3362): #6 _SwiperTimerMixin._onTimer (package:card_swiper/src/swiper.dart:391:24)
E/flutter ( 3362): #7 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
E/flutter ( 3362): #8 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
E/flutter ( 3362): #9 _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)