[PATCH] searchidx: deal with empty In-Reply-To and References headers

[Eric Wong <e@80x24.org>]

In some messages, these headers exist, but have empty values.
Do not let empty values throw off our search indexer to tie
threads together, as it can make non-sensical threads grouped
to a Message-Id of "" (empty string).

See
<https://public-inbox.org/git/11340844841342-git-send-email-mailing-lists.git@rawuncut.elitemail.org/raw>
for an example of such a message.

Thanks-to: Johannes Schindelin <Johannes.Schindelin@gmx.de>
  <https://public-inbox.org/git/alpine.DEB.2.20.1702041206130.3496@virtualbox/>
---
 Not fixed on the live sites, yet, but it will be once reindexing
 finishes (eatmydata public-inbox-index --reindex $GIT_DIR)

 lib/PublicInbox/SearchIdx.pm | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index d63dd7c..1142ca7 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -292,11 +292,15 @@ sub link_message {
 	my $mime = $smsg->{mime};
 	my $hdr = $mime->header_obj;
 	my $refs = $hdr->header_raw('References');
-	my @refs = $refs ? ($refs =~ /<([^>]+)>/g) : ();
+	my @refs = defined $refs ? ($refs =~ /<([^>]+)>/g) : ();
 	my $irt = $hdr->header_raw('In-Reply-To');
 	if (defined $irt) {
-		$irt = mid_clean($irt);
-		$irt = undef if $mid eq $irt;
+		if ($irt eq '') {
+			$irt = undef;
+		} else {
+			$irt = mid_clean($irt);
+			$irt = undef if $mid eq $irt;
+		}
 	}
 
 	my $tid;
-- 
EW