On line 69 (first line of tmpl.encode) I added this super simple patch to return an empty string instead of the string "undefined" when a specific value is not passed to the function.

if (!s) return '';

Figured I'd at least put it out here in case others are looking for the same thing, and maybe it's something you want to include (or know a more correct way for).

Thanks for a super simple-to-use, slim and awesome lib.