I accidentally mistyped a banner name ( wrong: https://meta.wikimedia.org/wiki/Special:CentralNoticeBanners/edit/stewvotes good: https://meta.wikimedia.org/wiki/Special:CentralNoticeBanners/edit/stewvote) and this is what I got:

[WlU8yQpAEK0AAE12AJUAAABR] 2018-01-09 22:06:01: Fatal exception of type "BannerExistenceException"

I feel CentralNotice should not fatal but display a message like "there's no such banner with that name" or something like that; instead of leaving people with the feeling they broke the wiki ;-)