Please be more informative when you can't encrypt to a list-admin

Schleuder 3.4.0-2+deb10u3 did sent this uninformative message (Subject: "Error"), when it couldn't find a matching key to one of the list-administrators.

No keys to encrypt to!
/usr/lib/ruby/vendor_ruby/mail/gpg/gpgme_helper.rb:17:in `encrypt'
/usr/lib/ruby/vendor_ruby/mail/gpg/encrypted_part.rb:23:in `initialize'
/usr/lib/ruby/vendor_ruby/schleuder/mail/encrypted_part.rb:10:in `initialize'
/usr/lib/ruby/vendor_ruby/mail/gpg.rb:43:in `new'
/usr/lib/ruby/vendor_ruby/mail/gpg.rb:43:in `block in encrypt'
/usr/lib/ruby/vendor_ruby/mail/gpg.rb:113:in `instance_eval'
/usr/lib/ruby/vendor_ruby/mail/gpg.rb:113:in `block in construct_mail'
/usr/lib/ruby/vendor_ruby/mail/message.rb:153:in `instance_eval'
/usr/lib/ruby/vendor_ruby/mail/message.rb:153:in `initialize'
/usr/lib/ruby/vendor_ruby/mail/mail.rb:51:in `new'
/usr/lib/ruby/vendor_ruby/mail/mail.rb:51:in `new'
/usr/lib/ruby/vendor_ruby/mail/gpg.rb:106:in `construct_mail'
/usr/lib/ruby/vendor_ruby/mail/gpg.rb:29:in `encrypt'
/usr/lib/ruby/vendor_ruby/schleuder/mail/gpg.rb:7:in `encrypt'
/usr/lib/ruby/vendor_ruby/mail/gpg/delivery_handler.rb:11:in `deliver_mail'
/usr/lib/ruby/vendor_ruby/mail/message.rb:260:in `deliver'
/usr/lib/ruby/vendor_ruby/schleuder/logger_notifications.rb:48:in `block in notify_admin'
/usr/lib/ruby/vendor_ruby/schleuder/logger_notifications.rb:29:in `each'
/usr/lib/ruby/vendor_ruby/schleuder/logger_notifications.rb:29:in `notify_admin'
/usr/lib/ruby/vendor_ruby/schleuder/logger_notifications.rb:13:in `error'
/usr/lib/ruby/vendor_ruby/schleuder/list.rb:356:in `rescue in block in send_to_subscriptions'
/usr/lib/ruby/vendor_ruby/schleuder/list.rb:347:in `block in send_to_subscriptions'
/usr/share/rubygems-integration/all/gems/activerecord-5.2.2.1/lib/active_record/relation/delegation.rb:71:in `each'
/usr/share/rubygems-integration/all/gems/activerecord-5.2.2.1/lib/active_record/relation/delegation.rb:71:in `each'
/usr/lib/ruby/vendor_ruby/schleuder/list.rb:346:in `send_to_subscriptions'
/usr/lib/ruby/vendor_ruby/schleuder/runner.rb:77:in `run'
/usr/lib/ruby/vendor_ruby/schleuder/cli.rb:36:in `work'
/usr/lib/ruby/vendor_ruby/thor/command.rb:27:in `run'
/usr/lib/ruby/vendor_ruby/thor/invocation.rb:126:in `invoke_command'
/usr/lib/ruby/vendor_ruby/thor.rb:369:in `dispatch'
/usr/lib/ruby/vendor_ruby/thor/base.rb:444:in `start'
/usr/bin/schleuder:13:in `<main>'

To debug, I made everyone a simple user but me. Once the problematic account was a simple user, schleuder would send:

The following error occurred while sending a message to  	user@example.org: No keys to encrypt to!