Fix: Remove warning

htdocs/contrat/class/contrat.class.php

@@ -553,7 +553,7 @@ class Contrat extends CommonObject
 				$line->desc           = $objp->description;
 				$line->qty            = $objp->qty;
 				$line->statut 		  = $objp->statut;
-				$line->ref            = $objp->ref;
+				$line->ref            = '';
 				$line->tva_tx         = $objp->tva_tx;
 				$line->localtax1_tx   = $objp->localtax1_tx;
 				$line->localtax2_tx   = $objp->localtax2_tx;