Show last answer result to user when dialog appears

[dgigafox]

Hi AppBrewery Team. First of all, thanks for the great tutorial. I hope you can take a look at this. This PR suggests the following changes:

• This moves Step 4 C and D inside Alert widget's DialogButton's onPressed
  property so that scoreKeeper and questionNumber will only reset state when
  the user confirms in the dialog box.

• This also styles the Alert widget to have an overlayColor of a more lighter color
  so when it appears, the icons are still visible.

[simplygkgk]

After inserting an Alert widget inside the setstate(), i get this message , otherwise everything works fine.
Please help

E/flutter (24316): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: NoSuchMethodError: The getter 'modalBarrierDismissLabel' was called on null.
E/flutter (24316): Receiver: null
E/flutter (24316): Tried calling: modalBarrierDismissLabel
E/flutter (24316): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
E/flutter (24316): #1 Alert.show (package:rflutter_alert/src/alert.dart:54:55)
E/flutter (24316): #2 _QuizPageState.checkAnswer. (package:quizlerapp/main.dart:41:16)
E/flutter (24316): #3 State.setState (package:flutter/src/widgets/framework.dart:1233:30)
E/flutter (24316): #4 _QuizPageState.checkAnswer (package:quizlerapp/main.dart:19:7)
E/flutter (24316): #5 _QuizPageState.build. (package:quizlerapp/main.dart:103:25)
E/flutter (24316): #6 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:779:19)
E/flutter (24316): #7 _InkResponseState.build. (package:flutter/src/material/ink_well.dart:862:36)
E/flutter (24316): #8 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (24316): #9 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:504:11)
E/flutter (24316): #10 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:282:5)
E/flutter (24316): #11 BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:217:7)
E/flutter (24316): #12 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:475:9)
E/flutter (24316): #13 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:76:12)
E/flutter (24316): #14 PointerRouter._dispatchEventToRoutes. (package:flutter/src/gestures/pointer_router.dart:122:9)
E/flutter (24316): #15 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
E/flutter (24316): #16 PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:120:18)
E/flutter (24316): #17 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:106:7)
E/flutter (24316): #18 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
E/flutter (24316): #19 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
E/flutter (24316): #20 GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (24316): #21 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (24316): #22 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (24316): #23 _rootRunUnary (dart:async/zone.dart:1196:13)
E/flutter (24316): #24 _CustomZone.runUnary (dart:async/zone.dart:1085:19)
E/flutter (24316): #25 _CustomZone.runUnaryGuarded (dart:async/zone.dart:987:7)
E/flutter (24316): #26 _invoke1 (dart:ui/hooks.dart:275:10)
E/flutter (24316): #27 _dispatchPointerDataPacket (dart:ui/hooks.dart:184:5)
E/flutter (24316):

[simplygkgk]

The Problem got resolved, as i had not defined Alert message in MaterialApp , therefore it was showing an error