diff --git a/Mpdf/Otl.php b/Mpdf/Otl.php
index 6cf7b7a..21526a9 100755
--- a/Mpdf/Otl.php
+++ b/Mpdf/Otl.php
@@ -6135,7 +6135,7 @@ class Otl
 		if ($available == '') {
 			return '';
 		}
-		$tags = preg_split('/-/', $ietf);
+		$tags = preg_split('/-/', $ietf ?? '');
 		$lang = '';
 		$country = '';
 		$script = '';