Failed assertion: boolean expression must not be null

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I/flutter ( 5599): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter ( 5599): The following assertion was thrown while handling a gesture:
I/flutter ( 5599): Failed assertion: boolean expression must not be null
I/flutter ( 5599):
I/flutter ( 5599): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter ( 5599): more information in this error message to help you determine and fix the underlying cause.
I/flutter ( 5599): In either case, please report this assertion by filing a bug on GitHub:
I/flutter ( 5599): https://github.com/flutter/flutter/issues/new?template=BUG.md
I/flutter ( 5599):
I/flutter ( 5599): When the exception was thrown, this was the stack:
I/flutter ( 5599): #0 _BottomPersonalizedDotBarState.build.. (package:bottom_personalized_dot_bar/bottom_personalized_dot_bar.dart:508:27)
I/flutter ( 5599): #1 State.setState (package:flutter/src/widgets/framework.dart:1148:30)
I/flutter ( 5599): #2 _BottomPersonalizedDotBarState.build. (package:bottom_personalized_dot_bar/bottom_personalized_dot_bar.dart:507:21)
I/flutter ( 5599): #3 DragGestureRecognizer._checkEnd. (package:flutter/src/gestures/monodrag.dart:439:41)
I/flutter ( 5599): #4 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
I/flutter ( 5599): #5 DragGestureRecognizer._checkEnd (package:flutter/src/gestures/monodrag.dart:439:5)
I/flutter ( 5599): #6 DragGestureRecognizer.didStopTrackingLastPointer (package:flutter/src/gestures/monodrag.dart:348:9)
I/flutter ( 5599): #7 OneSequenceGestureRecognizer.stopTrackingPointer (package:flutter/src/gestures/recognizer.dart:336:9)
I/flutter ( 5599): #8 DragGestureRecognizer._giveUpPointer (package:flutter/src/gestures/monodrag.dart:357:5)
I/flutter ( 5599): #9 DragGestureRecognizer.handleEvent (package:flutter/src/gestures/monodrag.dart:281:7)
I/flutter ( 5599): #10 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:76:12)
I/flutter ( 5599): #11 PointerRouter._dispatchEventToRoutes. (package:flutter/src/gestures/pointer_router.dart:117:9)
I/flutter ( 5599): #12 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
I/flutter ( 5599): #13 PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:115:18)
I/flutter ( 5599): #14 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:7)
I/flutter ( 5599): #15 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
I/flutter ( 5599): #16 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
I/flutter ( 5599): #17 GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
I/flutter ( 5599): #18 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
I/flutter ( 5599): #19 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
I/flutter ( 5599): #23 _invoke1 (dart:ui/hooks.dart:273:10)
I/flutter ( 5599): #24 _dispatchPointerDataPacket (dart:ui/hooks.dart:182:5)
I/flutter ( 5599): (elided 3 frames from package dart:async)
I/flutter ( 5599):
I/flutter ( 5599): Handler: "onEnd"
I/flutter ( 5599): Recognizer:
I/flutter ( 5599): HorizontalDragGestureRecognizer#cd9a0
I/flutter ( 5599): ════════════════════════════════════════════════════════════════════════════════════════════════════