diff --git a/sale.py b/sale.py
index a8d0614..06b3d78 100644
--- a/sale.py
+++ b/sale.py
@@ -2,6 +2,7 @@
 # The COPYRIGHT file at the top level of this repository contains the full
 # copyright notices and license terms.
 from decimal import Decimal
+from sql.operators import And
 from sql.aggregate import Sum
 from sql.conditionals import Coalesce
 
@@ -162,13 +163,14 @@ class Sale(metaclass=PoolMeta):
             condition=(sale.id == payline.sale)
             ).select(
                 sale.id,
-                where=((sale.total_amount_cache) & (
+                where=(And([
+                    sale.total_amount_cache != None,
                     sale.state.in_([
                         'draft',
                         'quotation',
                         'confirmed',
                         'processing',
-                        'done']))),
+                        'done'])])),
                 group_by=(sale.id),
                 having=(Operator(
                     sale.total_amount_cache - Sum(