bug#4229: 23.1; wrong-type arg: char or string-p, nil

[Chong Yidong]

> emacs -Q
> M-x set-variable debug-on-error t
> M-x load-file /......./bookmark.el
> C-x r l

> raises error:

> Debugger entered--Lisp error: (wrong-type-argument char-or-string-p nil)
>   insert(nil)
>   (prog1 (insert (bookmark-location bookmark)) (if (and ... ...)

I'm afraid I can't reproduce this.  Maybe you need a particular bookmark
file.  Could you try to make a stand-alone recipe?