Flutter 错误'；地图<；字符串，动态>'；，但是得到了一个类型'；空'；零安全状态下的颤振腹板

有没有关于如何调试颤振中的零错误的零安全性的建议

应为“Map”类型的值，但得到的值为“Null”类型

以防我用Map替换代码中的所有Map？但错误还在继续

由于采用了愚蠢的零安全实现方式，675行错误堆栈（下面的一行只是前300行）dos中没有一行包含错误源于Dart代码的信息

我99%确定该错误是由通信请求引起的，但该错误发生在我从对服务器的调用中得到响应之前，甚至没有到达转换地图对象的位置

不幸的是，这不是新的Flatter NULL safety第一次未能提供带有NULL对象错误的正确调试信息，但到目前为止，我设法通过将可执行代码减少到识别问题的程度来修复它们

Error: Expected a value of type 'Map<String, dynamic>', but got one of type 'Null'
at Object.throw_ [as throw] (http://localhost:5000/dart_sdk.js:5054:11)
at Object.castError (http://localhost:5000/dart_sdk.js:5013:15)
at Object.cast [as as] (http://localhost:5000/dart_sdk.js:5336:17)
at Function.as_C [as as] (http://localhost:5000/dart_sdk.js:4959:19)
at _engine.EngineSingletonFlutterWindow.new.handleNavigationMessage
(http://localhost:5000/dart_sdk.js:173578:52)
at handleNavigationMessage.next (<anonymous>)
at runBody (http://localhost:5000/dart_sdk.js:37456:34)
at Object._async [as async] (http://localhost:5000/dart_sdk.js:37487:7)
at _engine.EngineSingletonFlutterWindow.new.handleNavigationMessage
(http://localhost:5000/dart_sdk.js:173576:20)
at _engine.EnginePlatformDispatcher.__.[_sendPlatformMessage] (http://localhost:5000/dart_sdk.js:161799:68)
at _engine.EnginePlatformDispatcher.__.sendPlatformMessage (http://localhost:5000/dart_sdk.js:161627:33)
at _DefaultBinaryMessenger.[_sendPlatformMessage]
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:2096:38)
at _DefaultBinaryMessenger.send
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:2138:40)
at OptionalMethodChannel._invokeMethod
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:937:50)
at _invokeMethod.next (<anonymous>)
at runBody (http://localhost:5000/dart_sdk.js:37456:34)
at Object._async [as async] (http://localhost:5000/dart_sdk.js:37487:7)
at OptionalMethodChannel.[_invokeMethod]
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:935:20)
at OptionalMethodChannel.[_invokeMethod]
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:1042:34)
at OptionalMethodChannel.invokeMethod
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:1038:36)
at invokeMethod.next (<anonymous>)
at runBody (http://localhost:5000/dart_sdk.js:37456:34)
at Object._async [as async] (http://localhost:5000/dart_sdk.js:37487:7)
at OptionalMethodChannel.invokeMethod
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:1037:20)
at Function.selectSingleEntryHistory
(http://localhost:5000/packages/flutter/src/services/system_navigator.dart.lib.js:26:56)
at navigator$.NavigatorState.new.initState
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:24935:42)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51379:54)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatelessElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatelessElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatelessElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatelessElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatelessElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatelessElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatelessElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatelessElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatelessElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatelessElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatelessElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatelessElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatelessElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatelessElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatelessElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatelessElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatelessElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatelessElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.SingleChildRenderObjectElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.SingleChildRenderObjectElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.SingleChildRenderObjectElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:44756:29)
at framework.StatelessElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatelessElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatelessElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatelessElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatelessElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatelessElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatelessElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatelessElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatelessElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatelessElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatelessElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatelessElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatelessElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatelessElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatelessElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatelessElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatelessElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatelessElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.SingleChildRenderObjectElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.SingleChildRenderObjectElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.SingleChildRenderObjectElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:44756:29)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at _InheritedNotifierElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at _InheritedNotifierElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at _InheritedNotifierElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at _InheritedNotifierElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at _InheritedNotifierElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at _InheritedNotifierElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.InheritedElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.InheritedElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.InheritedElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.InheritedElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.InheritedElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.InheritedElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
at framework.StatefulElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
at framework.StatefulElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
at framework.StatefulElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51405:13)
at framework.StatefulElement.new.rebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
at framework.StatefulElement.new.[_firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51398:27)
at framework.StatefulElement.new.mount

错误：应为“Map”类型的值，但得到了“Null”类型的值
at Object.throw uu[as throw](http://localhost:5000/dart_sdk.js:5054:11)
在Object.castError(http://localhost:5000/dart_sdk.js:5013:15)
at Object.cast[作为](http://localhost:5000/dart_sdk.js:5336:17)
at Function.as_C[as as](http://localhost:5000/dart_sdk.js:4959:19)
at_engine.enginesingletonflatterwindow.new.handlenavigation消息
(http://localhost:5000/dart_sdk.js:173578:52)
在handleNavigationMessage.next（）处
在runBody(http://localhost:5000/dart_sdk.js:37456:34)
at对象。\u异步[作为异步](http://localhost:5000/dart_sdk.js:37487:7)
at_engine.enginesingletonflatterwindow.new.handlenavigation消息
(http://localhost:5000/dart_sdk.js:173576:20)
在[u engine.EnginePlatformDispatcher.[u sendPlatformMessage](http://localhost:5000/dart_sdk.js:161799:68)
在u engine.EnginePlatformDispatcher.\uuu.sendPlatformMessage(http://localhost:5000/dart_sdk.js:161627:33)
在[U DefaultBinaryMessenger.[U sendPlatformMessage]
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:2096:38)
在_DefaultBinaryMessenger.send
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:2138:40)
在OptionalMethodChannel.\u调用方法
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:937:50)
在_invokeMethod.next（）
在runBody(http://localhost:5000/dart_sdk.js:37456:34)
at对象。\u异步[作为异步](http://localhost:5000/dart_sdk.js:37487:7)
在OptionalMethodChannel上。[[u invokeMethod]
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:935:20)
在OptionalMethodChannel上。[[u invokeMethod]
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:1042:34)
在OptionalMethodChannel.invokeMethod
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:1038:36)
在invokeMethod.next（）处
在runBody(http://localhost:5000/dart_sdk.js:37456:34)
at对象。\u异步[作为异步](http://localhost:5000/dart_sdk.js:37487:7)
在OptionalMethodChannel.invokeMethod
(http://localhost:5000/packages/flutter/src/services/system_channels.dart.lib.js:1037:20)
在Function.selectSingleEntryHistory上
(http://localhost:5000/packages/flutter/src/services/system_navigator.dart.lib.js:26:56)
位于navigator$.NavigatorState.new.initState
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:24935:42)
位于framework.StatefulElement.new。[[u firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:51379:54)
位于framework.StatefulElement.new.mount
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
位于framework.inheriteElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
位于framework.inheriteElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
位于framework.inheriteElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
在framework.inheriteElement.new.rebuild处
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
位于framework.inheriteElement.new。[[u firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
在framework.inheriteElement.new.mount处
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
位于framework.inheriteElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
位于framework.inheriteElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
位于framework.inheriteElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
在framework.inheriteElement.new.rebuild处
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
位于framework.inheriteElement.new。[[u firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
在framework.inheriteElement.new.mount处
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30092:26)
位于framework.inheriteElement.new.inflateWidget
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28926:16)
位于framework.inheriteElement.new.updateChild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:28791:25)
位于framework.inheriteElement.new.performRebuild
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30128:31)
在framework.inheriteElement.new.rebuild处
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:29263:12)
位于framework.inheriteElement.new。[[u firstBuild]
(http://localhost:5000/packages/flutter/src/widgets/widget_span.dart.lib.js:30096:12)
在framework.inheriteElement.new.mount处
(http://localho