Click "add template", then "apply changes" without adding a template (or add one, then remove it.
Expected wikitext: none
Actual wikitext: <span property="mw:PageProp/noindex" data-mw="{"parts":[]}"></span>
We're clearly putting in a placeholder that we don't delete if the block is empty; because we don't display content blocks that don't render in read, you can't see these, which sucks and lets users do The Wrong Thing(tm).
Version: unspecified
Severity: normal