webdav via tramp failures and error

[ken <gebser@mousecar.com>]

Has anyone successfully used emacs to access a webdav server and edit 
documents on it?

Using <http://www.gnu.org/software/tramp/> as guidance, I tried opening 
an existing file for editing with "C-x C-f 
/dav:user@host:/var/www/html/webdave/index.html".  This "user" already 
has a password-protected account on this webdav server and has already 
logged into it with other apps (e.g., cadaver and the Gnome file 
manager) and created and edited files etc.

Moreover, tramp successfully connects to the same machine via ssh ("C-x 
C-f /ssh:user@host:/var/www/html/index.html") and allows the same user 
to edit documents outside of the webdav namespace.

So the failure isn't due to either networking or permissions.  Here's 
the emacs *Backtrace*:

Debugger entered--Lisp error: (void-function nil)
   nil(nil "dav" "user" "host")
   tramp-maybe-open-connection(nil "dav" "user" "host")
   tramp-send-command(nil "dav" "user" "host" "( test -d 
/var/www/html/webdav/index.html 2>/dev/null; echo tramp_exit_status $? )")
   tramp-send-command-and-check(nil "dav" "user" "host" "test -d 
/var/www/html/webdav/index.html" t)
 
tramp-handle-file-directory-p("/dav:user@host:/var/www/html/webdav/index.html")
   apply(tramp-handle-file-directory-p 
"/dav:user@host:/var/www/html/webdav/index.html")
   tramp-sh-file-name-handler(file-directory-p 
"/dav:user@host:/var/www/html/webdav/index.html")
   apply(tramp-sh-file-name-handler file-directory-p 
"/dav:user@host:/var/www/html/webdav/index.html")
   tramp-file-name-handler(file-directory-p 
"/dav:user@host:/var/www/html/webdav/index.html")
   file-directory-p("/dav:user@host:/var/www/html/webdav/index.html")
   find-file-noselect("/dav:user@host:/var/www/html/webdav/index.html" 
nil nil t)
   find-file("/dav:user@host:/var/www/html/webdav/index.html" t)
   call-interactively(find-file)