Narrow the conditions under which we allow a prop to be an empty string

larowlan → credited wim leers → .

larowlan → credited bnjmnm → .

Per the sequence of comments towards the end of 🐛 Hero component failed to render after removing text Active , this was de facto ready to go, but was split off into its own issue + MR — let's land it before it goes completely stale 😅

Green! Merging, per #7. Thanks, @larowlan and especially @bnjmnm!