Hello,

when using a dedicated GNUPG_HOMEDIR for the keys of a party's
participants, it's convenient if gpgparticipants-filter emits all keys
when no filter is provided.

The following patch implements this feature:

From e3d7d888e71643e0c77c6073cca707a4d9c230c0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <ukleinek@debian.org>
Date: Tue, 6 May 2025 19:02:19 +0200
Subject: [PATCH] gpgparticipants-filter: Make filter argument optional

Without arguments default to list all keys which matches the behavior
of `gpg --list-keys`.
---
 gpgparticipants/gpgparticipants-filter   | 22 ++++++++++------------
 gpgparticipants/gpgparticipants-filter.1 |  2 +-
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/gpgparticipants/gpgparticipants-filter b/gpgparticipants/gpgparticipants-filter
index 8899a28e2635..5e016dd31b85 100755
--- a/gpgparticipants/gpgparticipants-filter
+++ b/gpgparticipants/gpgparticipants-filter
@@ -79,7 +79,7 @@ class KeyDataSet:
         return self.valid_flag not in ['e', 'r']