can not run the app

[calystary]

when trying to run:
======== Exception caught by widgets library =======================================================
The following assertion was thrown building QuizPage(dirty, state: _QuizPageState#0c640):
A non-null String must be provided to a Text widget.
'package:flutter/src/widgets/text.dart':
Failed assertion: line 378 pos 10: 'data != null'

The relevant error-causing widget was:
QuizPage QuizPage:file:///C:/Users/lulu/Desktop/projects/angela/quizzler_flutter/lib/main.dart:16:20
When the exception was thrown, this was the stack:
#2 new Text (package:flutter/src/widgets/text.dart:378:10)
#3 _QuizPageState.build (package:quizzler/main.dart:45:22)
#4 StatefulElement.build (package:flutter/src/widgets/framework.dart:4870:27)
#5 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4754:15)
#6 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#7 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#8 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#9 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#10 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#11 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#12 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#13 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#14 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#15 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#16 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#17 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#18 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#19 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#20 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#21 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#22 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#23 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#24 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#25 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#26 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#27 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#28 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#29 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#30 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#31 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#32 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#33 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#34 RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:5787:32)
#35 MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6445:17)
#36 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#37 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#38 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#39 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#40 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#41 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#42 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#43 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#44 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#45 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#46 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#47 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#48 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#49 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#50 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#51 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#52 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#53 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#54 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#55 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#56 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#57 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#58 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#59 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#60 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#61 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#62 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#63 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#64 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#65 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#66 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#67 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#68 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#69 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#70 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#71 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#72 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#73 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#74 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#75 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#76 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#77 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#78 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#79 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#80 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#81 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#82 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#83 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#84 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#85 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#86 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#87 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#88 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#89 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#90 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#91 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#92 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#93 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#94 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#95 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#96 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#97 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#98 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#99 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#100 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#101 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#102 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#103 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#104 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#105 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#106 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#107 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#108 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#109 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#110 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#111 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#112 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#113 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#114 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#115 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#116 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#117 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#118 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#119 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#120 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#121 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#122 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#123 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#124 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#125 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#126 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#127 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#128 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#129 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#130 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#131 _InheritedNotifierElement.update (package:flutter/src/widgets/inherited_notifier.dart:111:11)
#132 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#133 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#134 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#135 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#136 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#137 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#138 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#139 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#140 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#141 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#142 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#143 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#144 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#145 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#146 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#147 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#148 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#149 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#150 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#151 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#152 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#153 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#154 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#155 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#156 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#157 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#158 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#159 StatelessElement.update (package:flutter/src/widgets/framework.dart:4834:5)
#160 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#161 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6291:14)
#162 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#163 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#164 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#165 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#166 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#167 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#168 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#169 ProxyElement.update (package:flutter/src/widgets/framework.dart:5108:5)
#170 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#171 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#172 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#173 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#174 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#175 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#176 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#177 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#178 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#179 StatefulElement.update (package:flutter/src/widgets/framework.dart:4960:5)
#180 Element.updateChild (package:flutter/src/widgets/framework.dart:3501:15)
#181 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4780:16)
#182 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4928:11)
#183 Element.rebuild (package:flutter/src/widgets/framework.dart:4477:5)
#184 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2659:19)
#185 WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:882:21)
#186 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:363:5)
#187 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1144:15)
#188 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1081:9)
#189 SchedulerBinding.scheduleWarmUpFrame. (package:flutter/src/scheduler/binding.dart:862:7)
(elided 6 frames from class _AssertionError, class _RawReceivePortImpl, class _Timer, and dart:async-patch)

[calystary]

didn't change nothing in the code, only wiped data in emulator, after that started working,