I'm running Perl v5.10.0 on Linux and I get the exact same output. I would assume, in a string context, an empty string to remain an empty string and not to become an "undefined value". An empty string is valid unicode (or indeed should be valid in any and every encoding) after all. I too am curious about the reason for this "feature", as I do a lot of unicode handling in my code – I've never noticed this before...