+ # It's obviously an error if the source user does not exist. It
+ # would also be an error if the destination domain didn't exist;
+ # however, DAViCal doesn't know about domains, so we let that slide.
+ raise NonexistentUserError.new(src.to_s()) if not user_exists(src)
+
+ # And it's an error if the destination user exists already.
+ raise UserAlreadyExistsError.new(dst.to_s()) if user_exists(dst)