diff --git a/dev/skeletons/build_class_from_table.php b/dev/skeletons/build_class_from_table.php
index d1ecc82e268..ff045901041 100644
--- a/dev/skeletons/build_class_from_table.php
+++ b/dev/skeletons/build_class_from_table.php
@@ -226,7 +226,7 @@ foreach($property as $key => $prop)
 		$varprop.="\t\t\$sql.= \" ";
 		if ($prop['istime'])
 		{
-			$varprop.='".(! isset($this->'.$prop['field'].') || strval($this->'.$prop['field'].')==\'\'?\'NULL\':$this->db->idate(';
+			$varprop.='".(! isset($this->'.$prop['field'].') || strlen($this->'.$prop['field'].')==0?\'NULL\':$this->db->idate(';
 			$varprop.="\$this->".$prop['field']."";
 			$varprop.='))."';
 			if ($i < sizeof($property)) $varprop.=",";
@@ -267,8 +267,8 @@ foreach($property as $key => $prop)
 		$varprop.=$prop['field'].'=';
 		if ($prop['istime'])
 		{
-			// (strval($this->datep)!='' ? "'".$this->db->idate($this->datep)."'" : 'null')
-			$varprop.='".(strval($this->'.$prop['field'].')!=\'\' ? "\'".$this->db->idate(';
+			// (strlen($this->datep)!=0 ? "'".$this->db->idate($this->datep)."'" : 'null')
+			$varprop.='".(strlen($this->'.$prop['field'].')!=0 ? "\'".$this->db->idate(';
 			$varprop.='$this->'.$prop['field'];
 			$varprop.=')."\'" : \'null\').';
 			$varprop.='"';
diff --git a/htdocs/contrat/contrat.class.php b/htdocs/contrat/contrat.class.php
index b3fc67f16e7..32c13bb9f2b 100644
--- a/htdocs/contrat/contrat.class.php
+++ b/htdocs/contrat/contrat.class.php
@@ -100,8 +100,8 @@ class Contrat extends CommonObject
 		$this->db->begin();
 
 		$sql = "UPDATE ".MAIN_DB_PREFIX."contratdet SET statut = 4,";
-		$sql.= " date_ouverture = '".$this->db->idate($date)."',";
-		if ($date_end) $sql.= " date_fin_validite = '".$this->db->idate($date_end)."',";
+		$sql.= " date_ouverture = ".(strlen($date)!=0?"'".$this->db->idate($date)."'":"null").",";
+		$sql.= " date_fin_validite = ".(strlen($date_end)!=0?"'".$this->db->idate($date_end)."'":"null").",";
 		$sql.= " fk_user_ouverture = ".$user->id.",";
 		$sql.= " date_cloture = null";
 		$sql.= " WHERE rowid = ".$line_id . " AND (statut = 0 OR statut = 3 OR statut = 5)";