I'm just starting to use notmuch so I'm not sure if this is the right
way to fix this but this was erroring out so I changed it to what you
see here which is working for me now.
---
 vim/notmuch.vim | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/vim/notmuch.vim b/vim/notmuch.vim
index 331e930..b33c6c6 100644
--- a/vim/notmuch.vim
+++ b/vim/notmuch.vim
@@ -653,7 +653,7 @@ ruby << EOF
 			items.each do |e|
 				authors = e.authors.to_utf8.split(/[,|]/).map { |a| author_filter(a) }.join(",")
 				date = Time.at(e.newest_date).strftime(date_fmt)
-				subject = e.messages.first['subject']
+				subject = e.subject
 				if $mail_installed
 					subject = Mail::Field.new("Subject: " + subject).to_s
 				else
-- 
1.9.3