Fix for "Cannot read properties of null (reading 'classList')" Sentry issue

[latata]

• removing @ts-strict-ignore comments from two files
• adding a null-check for slot element

Sentry issue: https://fandom-lf.sentry.io/issues/5043089866/?environment=preview&project=4506854504923136&query=is:unresolved+adengine:True+!external:True&sort=freq&statsPeriod=7d&stream_index=0