Someone was editing the Tag Wiki for jRuby, and it came out blank when I approved the edit. Looks like the Excerpt section is required; if it is left out, the Body section is still there in the edits history, but it is not shown in the Tag Wiki.
I fixed this, we now validate that the excerpt is not blank when suggested.
There is a slight edge condition:
If somebody submits a tag wiki edit for a blank wiki and only the wiki body is accepted (wiki excerpt rejected) the wiki will still appear blank. No information is lost in this case, and the next editor will see the body.
However, there is no longer a way for regular users to blank out a tag wiki (unless they have full tag wiki edit privs and decide to roll back the excerpt)