suppress undefined warnings in cycle death

diff --git a/lib/Text/Tradition/Collation.pm b/lib/Text/Tradition/Collation.pm
index 5e38422..4c410c1 100644 (file)
--- a/lib/Text/Tradition/Collation.pm
+++ b/lib/Text/Tradition/Collation.pm
@@ -1493,8 +1493,8 @@ sub calculate_ranks {
             $r->rank( $node_ranks->{$rel_containers{$r->id}} );
         } else {
                # Die. Find the last rank we calculated.
-               my @all_defined = sort { $node_ranks->{$rel_containers{$a->id}}
-                                <=> $node_ranks->{$rel_containers{$b->id}} }
+               my @all_defined = sort { ( $node_ranks->{$rel_containers{$a->id}}||-1 )
+                                <=> ( $node_ranks->{$rel_containers{$b->id}}||-1 ) }
                        $self->readings;
                my $last = pop @all_defined;
             throw( "Ranks not calculated after $last - do you have a cycle in the graph?" );