'Null check operator used on a null value' when run release mode

[hunghanguyen]

I/flutter (12570): Null check operator used on a null value
I/flutter (12570): #0 Runtime.executeLib (package:dart_eval/src/eval/runtime/runtime.dart:454)
I/flutter (12570): #1 _EvalWidgetState.build (package:flutter_eval/src/flutter_eval.dart:372)
I/flutter (12570): #2 StatefulElement.build (package:flutter/src/widgets/framework.dart:5080)
I/flutter (12570): #3 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4968)
I/flutter (12570): #4 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:5133)
I/flutter (12570): #5 Element.rebuild (package:flutter/src/widgets/framework.dart:4690)
I/flutter (12570): #6 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2743)
I/flutter (12570): #7 WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:863)
I/flutter (12570): #8 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:381)
I/flutter (12570): #9 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1289)
I/flutter (12570): #10 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1218)
I/flutter (12570): #11 SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1076)
I/flutter (12570): #12 _invoke (dart:ui/hooks.dart:145)
I/flutter (12570): #13 PlatformDispatcher._drawFrame (dart:/u/i/platform_dispatcher.dart:338)
I/flutter (12570): #14 _drawFrame (dart:ui/hooks.dart:112)

Hi, when i run your demo project with release mode ide show error. how to i fix it?
Thanks