diff --git a/htdocs/expedition/class/expedition.class.php b/htdocs/expedition/class/expedition.class.php
index 7454e0b7832..dac6efee52c 100644
--- a/htdocs/expedition/class/expedition.class.php
+++ b/htdocs/expedition/class/expedition.class.php
@@ -3050,7 +3050,8 @@ class ExpeditionLigne extends CommonObjectLine
 		// update lot
 
 		if (!empty($batch) && isModEnabled('productbatch')) {
-			dol_syslog(get_class($this)."::update expedition batch id=$expedition_batch_id, batch_id=$batch_id, batch=$batch");
+			$batch_id_str = $batch_id ?? 'null';
+			dol_syslog(get_class($this)."::update expedition batch id=$expedition_batch_id, batch_id=$batch_id_str, batch=$batch");
 
 			if (empty($batch_id) || empty($this->fk_product)) {
 				dol_syslog(get_class($this).'::update missing fk_origin_stock (batch_id) and/or fk_product', LOG_ERR);