23.0.50; vc-checkin from vc-dired buffer gives (wrong-type-argument stringp nil)

[Tim Van Holder <tim.vanholder@gmail.com>]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the emacs-pretest-bug@gnu.org mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

- C-x v d to open a dired buffer for a directory containing changed
  files (CVS-controlled in my case)
- v = -> works fine, shows diff
- v v -> errors out with (wrong-type-argument stringp nil)

The error seems to be that vc-parent-buffer is nil, which makes sense
since vc-start-entry uses get-file-buffer to set it, and when in dired
mode there is no live buffer for the file yet.

In GNU Emacs 23.0.50.1 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2007-11-09 on leeloo
Windowing system distributor `RealVNC Ltd', version 11.0.3370
configured using `configure  '--with-gtk' '--with-xpm' '--with-jpeg' '--with-gif' '--with-tiff' '--with-png' '--with-x' '--with-kerberos' '--with-kerberos5''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

Major mode: Dired under CVS

Minor modes in effect:
  whitespace-global-mode: t
  show-paren-mode: t
  pc-selection-mode: t
  display-time-mode: t
  delete-selection-mode: t
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t