Error class

models/sale.py

@@ -45,7 +45,7 @@ class SaleOrder(models.Model):
     # ------------------------------------------------------
     @api.multi
     def _prepare_invoice(self):
-        values = super(saleOrder, self)._prepare_invoice()
+        values = super(SaleOrder, self)._prepare_invoice()
         values.update({
             'user_second_id': self.user_second_id.id or False,
         })