Null check operator used on a null value

I get this error sometimes

Null check operator used on a null value
The relevant error-causing widget was

Swiper
lib/views/cards_view.dart:36
When the exception was thrown, this was the stack
#0      _StackViewState._updateValues
package:flutter_card_swipper/src/swiper.dart:864

#1      _StackViewState.didUpdateWidget
package:flutter_card_swipper/src/swiper.dart:874
#2      StatefulElement.update
package:flutter/…/widgets/framework.dart:4682
#3      Element.updateChild
package:flutter/…/widgets/framework.dart:3293
#4      ComponentElement.performRebuild
package:flutter/…/widgets/framework.dart:4520

This is the offending function, I suppose _swiperWidth is null:

void _updateValues() {
  if (widget.scrollDirection == Axis.horizontal) {
    final double space = (_swiperWidth! - widget.itemWidth!) / 2;
    offsets = [-space, -space / 3 * 2, -space / 3, 0.0, _swiperWidth];
  } else {
    final double space = (_swiperHeight! - widget.itemHeight!) / 2;
    offsets = [-space, -space / 3 * 2, -space / 3, 0.0, _swiperHeight];
  }
}

flutter doctor -v

[✓] Flutter (Channel stable, 2.0.6, on macOS 11.2.3 20D91 darwin-x64, locale en-GB)
    • Flutter version 2.0.6 at /Users/dennis/flutter
    • Framework revision 1d9032c7e1 (3 weeks ago), 2021-04-29 17:37:58 -0700
    • Engine revision 05e680e202
    • Dart version 2.12.3

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Users/dennis/Library/Android/sdk
    • Platform android-30, build-tools 30.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.5, Build version 12E262
    • CocoaPods version 1.10.1

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] Connected device (4 available)
    • iPhone 8 Plus (mobile) • 16007D4D-626C-4001-8AAA-D2FE317EE7E7 • ios            • com.apple.CoreSimulator.SimRuntime.iOS-14-5 (simulator)
    • iPhone 11 (mobile)     • 200809FD-F24E-44C7-8886-05EFF2DD3CDA • ios            • com.apple.CoreSimulator.SimRuntime.iOS-14-5 (simulator)
    • macOS (desktop)        • macos                                • darwin-x64     • macOS 11.2.3 20D91 darwin-x64
    • Chrome (web)           • chrome                               • web-javascript • Google Chrome 90.0.4430.212

[amondnet]

@DenisBarzanov
I have the same issue. So I changed it to the package below.

flutter_swiper:
  git:
    url: git@github.com:Arkangel12/flutter_swiper.git
    ref: master

best-flutter/flutter_swiper#264

[SalahAdDin]

Well, i have this one too:

======== Exception caught by widgets library =======================================================
The following assertion was thrown building Swiper(dirty, state: _SwiperState#d8d2c):
'package:flutter_card_swipper/src/swiper.dart': Failed assertion: line 704 pos 16: 'itemWidth != null && itemHeight != null': is not true.

The relevant error-causing widget was: 
  Swiper file:///home/luisalaguna/Projects/cancer/thesis_cancer/lib/features/content/presentation/widgets/post.dart:28:15
When the exception was thrown, this was the stack: 
#2      new _TinderSwiper (package:flutter_card_swipper/src/swiper.dart:704:16)
#3      _SwiperState._buildSwiper (package:flutter_card_swipper/src/swiper.dart:526:14)
#4      _SwiperState.build (package:flutter_card_swipper/src/swiper.dart:587:27)
#5      StatefulElement.build (package:flutter/src/widgets/framework.dart:4691:27)
#6      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4574:15)
...
====================================================================================================

[SalahAdDin]

It is not logical to have and assertion if we are working with null safety, I think.

[pzentenoe]

I'm sorry guys I've been too busy in my work I haven't been able to evolve this package, for now I see it difficult, can you send me a pull request, I'll be happy to review it.
Best regards