A new feature on SO is that if you have a link to jsfiddle but no code, the system prevents you from posting, saying "Links to jsfiddle.net must be accompanied by code"
However, this error message also appears if you start editing and add the link, but then click on Cancel to opt out of your edits!
Edit: I don't always get the error message though. It seems to depend on which answer I'm trying to edit. Need more testing.
More edit: Yes, of course the error message does not appear for answers that have one or more words backticked (which count as code. Duh).