mouse-buffer-menu signals wrong-type-argument

[Kalle Olavi Niemitalo]

In GNU Emacs 20.7.2 (i386-debian-linux-gnu, X toolkit)
 of Sun May  6 2001 on Astalo modified by Debian
configured using `configure  i386-debian-linux-gnu --prefix=/usr 
--sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib 
--infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --with-x=yes 
--with-x-toolkit=yes'

1. Start Emacs with -q --no-site-file.

2. Set mouse-buffer-menu-mode-mult to 0.
   M-: (setq mouse-buffer-menu-mode-mult 0) RET

3. Create a buffer "a" and start Lisp mode.
   C-x b a RET
   M-x lisp-mode RET

4. Create a buffer "b" and start C mode.
   C-x b b RET
   M-x c-mode RET

5. Kill the *scratch* and *Messages* buffers.
   C-x k *scratch* RET
   C-x k *Messages* RET

6. Start `mouse-buffer-menu'.
   C-down-mouse-1

7. Emacs gives an error:
   Wrong type argument: consp, nil

I originally got the error with a much larger set of buffers;
I hope this smaller set is easier for you to reproduce.