diff --git a/modules/purchase_trade/lot.py b/modules/purchase_trade/lot.py
index fca5fe1..c35bfcd 100755
--- a/modules/purchase_trade/lot.py
+++ b/modules/purchase_trade/lot.py
@@ -2898,17 +2898,21 @@ class LotInvoiceStart(ModelView):
             })
 
     @fields.depends('type')
-    def on_change_with_action(self, name=None):
-        if self.lot_p and self.type == 'purchase':
-            if self.lot_p[0].lot.line.purchase.wb.qt_type in [e.quantity_type for e in self.lot_p[0].lot.lot_hist]:
-                return 'final'
-            else:
-                return 'prov'
-        if self.lot_s and self.type == 'sale':
-            if self.lot_s[0].lot.sale_line.sale.wb.qt_type in [e.quantity_type for e in self.lot_s[0].lot.lot_hist]:
-                return 'final'
-            else:
-                return 'prov'
+    def on_change_with_action(self, name=None):
+        if self.lot_p and self.type == 'purchase':
+            purchase = getattr(getattr(self.lot_p[0].lot, 'line', None), 'purchase', None)
+            wb = getattr(purchase, 'wb', None)
+            if wb and wb.qt_type in [e.quantity_type for e in self.lot_p[0].lot.lot_hist]:
+                return 'final'
+            else:
+                return 'prov'
+        if self.lot_s and self.type == 'sale':
+            sale = getattr(getattr(self.lot_s[0].lot, 'sale_line', None), 'sale', None)
+            wb = getattr(sale, 'wb', None)
+            if wb and wb.qt_type in [e.quantity_type for e in self.lot_s[0].lot.lot_hist]:
+                return 'final'
+            else:
+                return 'prov'
             
     @fields.depends('lot_p','type','quantity')
     def on_change_with_quantity(self, name=None):