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

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<tr><td><span title='2021-11-19 23:04:19 +0100'>2021-11-19</span></td><td><a href='/guix/commit/nix/libutil?id=24224530d1f4a70808d003ba8dce849b77625b79'>daemon: Micro-optimize 'deletePath'.</a><span class='msg-avail'>...<span class='msg-tooltip'>'remove' calls 'unlink' first and falls back to 'rmdir' upon EISDIR.
This change gets rid of the 'unlink' call for every directory being
removed.

* nix/libutil/util.cc (_deletePath): Call 'unlink' or 'rmdir' depending
on 'st.st_mode', rather than call 'remove'.
</span></span></td><td>Ludovic Courtès</td></tr>