Add null safe operator when calling any method on $query

Thanks for reporting this problem, and sorry it took me so long to respond!

As in the other issue ( 🐛 Call to a member function addTag() on null in Drupal\search_api\Plugin\views\cache\SearchApiTimeCache->alterCacheMetadata() Closed: duplicate ), though, please try to find the root cause, not just propose fixing the symptoms. (And also please use patches instead of MRs.)
Finally, we do not depend on PHP 8 yet, so we’d either have to wait for that (probably when Drupal 9 isn’t supported anymore) or change the patch accordingly.

Now that I saw 🐛 Call to a member function preExecute() on null in SearchApiTimeCache::generateResultsKey() Needs work , I’d say this is just a duplicate, better to fix all of this in one issue.