Project in a broken state

[cdn34]

Flutter 1.23.0-8.0.pre.137 • channel master • https://github.com/flutter/flutter.git
Framework • revision ece2f98eb0
Engine • revision a8d7d97bef
Tools • Dart 2.11.0 (build 2.11.0-185.0.dev)

Lots of errors in the project in the starter branch

Several instance where these errors occurs:
Undefined name 'standardEasing'
Undefined name 'Router'.
The method 'ChildBackButtonDispatcher' isn't defined for the type '_MailRouter'.
The name 'RootBackButtonDispatcher' isn't a type, so it can't be used in an 'as' expression.
The method 'Router' isn't defined for the type '_MailRouter'.
Mixin can only be applied to class.
Classes can only mix in mixins and classes.
Classes can only extend other classes.
Undefined class 'RouteInformation'.
The method 'RouteInformation' isn't defined for the type 'ReplyRouteInformationParser'.