Ionic lab doesn’t work anymore. Here is the message I get

Ionic Framework Ionic Angular
1 
$ionic serve --lab

ng.cmd run app:serve --host=localhost --port=8100 [ng] Schema validation failed with the following errors: [ng] Data path “.builders[‘app-shell’]” should have required property ‘class’.

 [ERROR] ng has unexpectedly closed (exit code 1).

    The Ionic CLI will exit. Please check any output above for error details.