This patch has been proposed upstream:
https://lists.systemreboot.net/guile-email/87mtnv1r2p.fsf@gnu.org/T/#u.

From c21fe0f0e28b80b606973d3e372e2bc8528c9766 Mon Sep 17 00:00:00 2001
From: Mathieu Othacehe <othacehe@gnu.org>
Date: Wed, 29 Sep 2021 12:47:35 +0000
Subject: [PATCH 1/1] email: Do not use an empty bytevector to test the
 charset.

Using an empty bytevector no longer throws an exception since this Guile
commit: 5ea8c69e9153a970952bf6f0b32c4fad6a28e839.

* email/email.scm (post-process-content-transfer-encoding): Use a bytevector
containg the 'e' character to test the charset validity.
---
 email/email.scm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/email/email.scm b/email/email.scm
index 3f4e194..ac70463 100644
--- a/email/email.scm
+++ b/email/email.scm
@@ -832,7 +832,8 @@ values. The returned headers is a string and body is a bytevector."
   (define (valid-charset? charset)
     (catch #t
       (lambda ()
-        (bytevector->string (make-bytevector 0 0) charset)
+        ;; Try to convert a bytevector containg the 'e' character.
+        (bytevector->string (make-bytevector 1 48) charset)
         #t)
       (const #f)))
 
-- 
2.33.0

u/services/sddm.scm'>log</a><a href='/guix/tree/gnu/services/sddm.scm?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>tree</a><a href='/guix/commit/gnu/services/sddm.scm?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>commit</a><a href='/guix/diff/gnu/services/sddm.scm?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/sddm.scm'>
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<div class='path'>path: <a href='/guix/log/?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>root</a>/<a href='/guix/log/gnu?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>gnu</a>/<a href='/guix/log/gnu/services?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>services</a>/<a href='/guix/log/gnu/services/sddm.scm?id=dce5845a66303ddcb8d70259557d79dee473f0ac'>sddm.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/services/sddm.scm?id=dce5845a66303ddcb8d70259557d79dee473f0ac&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-03-19 18:52:16 +0800'>2024-03-19</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=3ea55fada0593cd05c686cef2f6a59ba65933ef5'>services: sddm: Add extension for localed-service-type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sddm.scm (sddm-service-type): Add extension for
localed-service-type.
* gnu/services/xorg.scm (xorg-configuration-keyboard-layout): Export it.

Change-Id: I26e6475b733d69f1baf00786e302a3ec6d3c4a74
Signed-off-by: 宋文武 &lt;iyzsong@member.fsf.org&gt;
</span></span></td><td>Zheng Junjie</td></tr>
<tr><td><span title='2023-08-02 22:27:43 +0800'>2023-08-02</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=7e056197d7bf8f888fe52db9d5ee34ec253ffff9'>services: sddm: Set some environment variables for the breeze theme.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sddm.scm (sddm-service-type): Pass #:environment-variables to
make-forkexec-constructor.

Signed-off-by: 宋文武 &lt;iyzsong@member.fsf.org&gt;
</span></span></td><td>Zheng Junjie</td></tr>
<tr><td><span title='2023-05-11 13:21:45 +0200'>2023-05-11</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=2df5d4fd18a2fbcb8066a50e2da8ec64635f5162'>system: pam: Let PAM extensions add shepherd requirements.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/pam.scm (&lt;pam-extension&gt;): New record type.
(pam-shepherd-service): Add Shepherd synchronization point.

* gnu/services/mail.scm (dovecot-shepherd-service)
* gnu/services/lightdm.scm (lightdm-shepherd-service)
* gnu/services/mail.scm (opensmtpd-shepherd-service)
* gnu/services/sddm.scm (sddm-shepherd-service)
* gnu/services/ssh.scm (lsh-shepherd-service, openssh-shepherd-service)
* gnu/services/xorg.scm (slim-shepherd-service, gdm-shepherd-service)
* gnu/services/base.scm (greetd-shepherd-services): Add PAM requirement.

* gnu/system/pam.scm (/etc-entry, extend-configuration,
pam-root-service-type, pam-root-service)
* gnu/services/authentication.scm (pam-ldap-pam-service)
* gnu/services/base.scm (pam-limits-service-type)
(greetd-pam-service)
* gnu/services/desktop.scm (pam-gnome-keyring)
* gnu/services/kerberos.scm (pam-krb5-pam-service)
* gnu/services/pam-mount.scm (pam-mount-pam-service): Adapt to use
pam-extension.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Josselin Poiret</td></tr>
<tr><td><span title='2023-04-07 17:56:55 +0200'>2023-04-07</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=aeb5df82dddfa84d91afd4373189d968e6377574'>services: sddm: Remove 'sddm-service' procedure.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sddm.scm (sddm-service): Remove procedure.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2020-11-18 22:31:32 +0100'>2020-11-18</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=0ae9bbe4f5f89e6f597bdb1f6df646fc5f504876'>services: SDDM: Wait for elogind before starting.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/44669&gt;.

* gnu/services/sddm.scm (sddm-shepherd-service)[requirement]: Add elogind.
</span></span></td><td>Marius Bakke</td></tr>