diff --git a/invoice.py b/invoice.py
index 6539ba9..3340340 100644
--- a/invoice.py
+++ b/invoice.py
@@ -15,7 +15,7 @@ class Invoice(metaclass=PoolMeta):
         }
 
 
-    account_analytic = fields.Many2One('analytic_account.account', 'Analytic Account', required=True,
+    account_analytic = fields.Many2One('analytic_account.account', 'Analytic Account',
                                        domain=[('type', '=', 'normal')],
                                        states=_states)
 
diff --git a/sale.py b/sale.py
index 0dd2ce0..49836fc 100644
--- a/sale.py
+++ b/sale.py
@@ -15,6 +15,7 @@ class Sale(metaclass=PoolMeta):
                                        domain=[
                                            ('type', '=', 'normal'),
                                        ])
+
 class SaleLine(metaclass=PoolMeta):
     'Sale Line Analytic Operation'
     __name__ =  'sale.line'