bug#68671: 30.0.50; C-x 8 e s RET persistently breaks C-x 8 e r

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 23 Jan 2024 11:59:41 +0100
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 
> 1. emacs -Q
> 2. C-x 8 e s RET
>    [ i.e. invoke `emoji-search` and exit with an empty minibuffer ]
> 3. Observe error "Wrong type argument: char-or-string-p, nil".  This
>    error message could be more friendly, but that's not the issue here.
> 4. C-x 8 e r
> 5. Observe error "Wrong type argument: stringp, nil".  That's the issue.
> 
> What happens is that C-x 8 e s RET adds `nil` to the value of
> `emoji--recent`, which breaks subsequent C-x 8 e r (`emoji-recent`).
> This is extra troublesome because `emoji--recent` is used as a
> multisession variable, so simply restarting Emacs doesn't help.
> 
> I see this also with Emacs 29.2, FWIW.

Thanks.  Patches for fixing this will be most welcome.