bug#42589: 26.3; "Wrong type argument: stringp, nil"

[Alan Mackenzie <acm@muc.de>]

Hello, Drew.

In article <mailman.218.1595971504.2739.bug-gnu-emacs@gnu.org> you wrote:
> emacs -Q

> `M-x load-library dired-x'

> `C-x d' for a dir that has a subdir

> With cursor on a subdir line, `i', to insert its listing.

> With cursor on the inserted-subdir heading line: `!'.

> You get that raw error message.

> `!' is not intended for directory heading lines.  But the error
> raised shouldn't be one you see.

Yes, I've tried this in 26.3, and the error you've described is there.
However, in master, this bug has been fixed.

I haven't tried it in Emacs 27 yet, but if it's not fixed there yet,
it's likely too late to fix it now.

> In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
>  of 2019-08-29
> Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
> Windowing system distributor `Microsoft Corp.', version 10.0.18362
> Configured using:
>  `configure --without-dbus --host=x86_64-w64-mingw32
>  --without-compress-install 'CFLAGS=-O2 -static -g3''

-- 
Alan Mackenzie (Nuremberg, Germany).