`where-is` was looking for empty string return values from `completing-read` and swapping in a default value in that case. Updated now to use the default-handling mechanism provided by `completing-read`, rather than recreating it. This also provides a bit of extra capability because now the user can insert the default value into the minibuffer (for modification) via `next-history-element` (so-called "future history", described in the elisp manual). -- Cameron Desautels