sendmail-sync-aliases pass nil to file-attributes which cant handle it

[Matthias Teege]

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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 address@hidden mailing list.

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

(setq mail-personal-alias-file nil)
(compose-mail)

gives a (wrong-type-argument stringp nil) because
(sendmail-sync-aliases) in sendmail.el passes nil to
(file-attributes) which cant handle it.

The variable mail-personal-alias-file is documented as followos

"*If non-nil, the name of the user's personal mail alias file.
This file typically should be in same format as the `.mailrc' file used by
the `Mail' or `mailx' program.
This file need not actually exist."

This implies, that I can set mail-personal-alias-file to nil, which
disables the reading auf "~/.mailrc".

If is set mail-personal-alias-file to "" compose-mail works without
any error.

In GNU Emacs 21.3.50.2 (i386-unknown-freebsd4.8, X toolkit, Xaw3d scroll bars)
 of 2003-03-08 on gic.mteege.de
configured using `configure '--prefix=/usr/home/matthias/my''

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: de_DE.ISO8859-1
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t