URL for single items

Hi,

Sorry I have looked around and can't find an answer so sorry if I missed this in the docs but I am struggling with the "URL for single items"

After re writing my urls from /content?item=whatever it's now /content/whatever

I have tried to add this to the URL for single items field in region options as /content/{slug} but it's chucking out an error of

Notice: Undefined variable: details in /Users/macbookpro/Documents/Sites/dickjohns/perch/core/apps/content/modes/region.options.post.php on line 11

I assumed this worked the same as it does for blogs. Can someone point me in the right direction please :)

Thanks!