Ionic serve with ionic 4 in ubuntu

i have installled ionic 4 cli and created tabs app. while serving file i was getting this error.

ionic serve
> ng 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).