Improved forward index
diff --git a/lib/Krawfish/Koral/Document.pm b/lib/Krawfish/Koral/Document.pm
index 96f7378..cfad1f3 100644
--- a/lib/Krawfish/Koral/Document.pm
+++ b/lib/Krawfish/Koral/Document.pm
@@ -169,7 +169,7 @@
# Get the term surface from the primary text
# TODO:
# Ensure that the offsets are valid!
- my $preceding = substr($primary, $primary_index, $start - $primary_index);
+ my $preceding = substr($primary, $primary_index, $start - $primary_index) // '';
my $term = substr($primary, $start, $end - $start);
$primary_index = $end;