dired-at-point: Wrong type argument: stringp, nil

[Hiroshi Fujishima]

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

(1) emacs -q
(2) M-x ffap-bindings
(3) C-x d ~non-exist-user RET

cause following error.

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  file-writable-p(nil)
  dired-at-point()
  call-interactively(dired-at-point)

In GNU Emacs 21.3.50.1 (sparc-sun-solaris2.8, X toolkit, Xaw3d scroll bars)
 of 2004-02-10 on newton.nature.tsukuba.ac.jp
configured using `configure '--prefix=/usr/local/emacs21' '--without-xim' 
'CFLAGS=-O3' 'CPPFLAGS=-I/usr/local/emacs21/include -I/usr/misc/include' 
'LDFLAGS=-L/usr/local/emacs21/lib -R/usr/local/emacs21/lib''

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: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  iswitchb-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
( s e t q SPC m a i l - u s e r - a g <escape> <tab> 
SPC ' g n u s - u s e <escape> <tab> ) <escape> x g 
n u s <return> n n C-x b m e s <return> C-x b g r <return> 
C-x b s c r <return> C-j <escape> x r e p o r <tab> 
<return>

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