Null check operator used on a null value

[vmeretin]

Non-fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: Null check operator used on a null value. Error thrown Instance of 'ErrorDescription'.
       at State.setState(framework.dart:1108)
       at _FlutterSliderState._rightHandlerMove(flutter_xlider.dart:1303)
       at _FlutterSliderState._rightHandlerWidget.<fn>(flutter_xlider.dart:1621)
       at RenderPointerListener.handleEvent(proxy_box.dart:2831)
       at GestureBinding.dispatchEvent(binding.dart:419)
       at RendererBinding.dispatchEvent(binding.dart:287)
       at GestureBinding._handlePointerEventImmediately(binding.dart:374)
       at GestureBinding.handlePointerEvent(binding.dart:338)
       at GestureBinding._flushPointerEventQueue(binding.dart:296)
       at GestureBinding._handlePointerDataPacket(binding.dart:279)

We use version from master branch

[vmeretin]

Non-fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: Null check operator used on a null value. Error thrown Instance of 'ErrorDescription'.
       at AnimationController.stop(animation_controller.dart:777)
       at AnimationController.value=(animation_controller.dart:364)
       at AnimationController.reset(animation_controller.dart:385)
       at _FlutterSliderState._stopHandlerAnimation(flutter_xlider.dart:1719)
       at _FlutterSliderState._leftHandlerWidget.<fn>(flutter_xlider.dart:1530)
       at RenderPointerListener.handleEvent(proxy_box.dart:2833)
       at GestureBinding.dispatchEvent(binding.dart:419)
       at RendererBinding.dispatchEvent(binding.dart:287)
       at GestureBinding._handlePointerEventImmediately(binding.dart:374)
       at GestureBinding.handlePointerEvent(binding.dart:338)
       at GestureBinding._flushPointerEventQueue(binding.dart:296)
       at GestureBinding._handlePointerDataPacket(binding.dart:279)