remove conditional for generate commission from return sales

invoice.py

@@ -10,8 +10,7 @@ from trytond.model import fields
 __all__ = ['Invoice']
 
 
-class Invoice:
-    __metaclass__ = PoolMeta
+class Invoice(metaclass=PoolMeta):
     __name__ = 'account.invoice'
     commission = fields.Float('Commission', states={
         'readonly': True
@@ -25,6 +24,7 @@ class Invoice:
                 commissions.extend(invoice.create_commission_by_percentage())
             else:
                 commissions.extend(super(Invoice, cls).create_commissions([invoice]))
+
         return commissions
 
     def create_commission_by_percentage(self):
@@ -35,7 +35,7 @@ class Invoice:
         amount = self.untaxed_amount * Decimal(percentage / 100.0)
         digits = Commission.amount.digits
         exp = Decimal(str(10.0 ** -digits[1]))
-        if amount > 0:
+        if amount != 0:
             record = {
                 'agent': self.agent.id,
                 'product': self.agent.plan.commission_product,