From 73970c8dda21c4df13373b03caede6273ff81e4c Mon Sep 17 00:00:00 2001
From: Kohaku-Blueleaf <59680068+KohakuBlueleaf@users.noreply.github.com>
Date: Sat, 17 Oct 2026 20:18:32 +0800
Subject: [PATCH 1/2] Fix startswith_fws to check for non-empty list
 (gh-159621)

Avoid access empty tokenlist reported in gh-159621
---
 Lib/email/_header_value_parser.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index f396f4f9b32a9a8..9c1f99b1615f61c 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -155,7 +155,7 @@ def all_defects(self):
         return sum((x.all_defects for x in self), self.defects)
 
     def startswith_fws(self):
-        return self[0].startswith_fws()
+        return self and self[0].startswith_fws()
 
     as_ew_allowed = True
 

From 136548f6ca49eee270572aa8c6271125ac2d4c66 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Sun, 18 Oct 2026 05:47:57 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst

diff --git a/Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst b/Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst
new file mode 100644
index 000000000000000..e744bfe1b75579f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst
@@ -0,0 +1,2 @@
+Fix an :exc:`IndexError` in :mod:`email` when folding address headers
+containing empty comments.