Import account_invoice exception when needed

account_invoice is an extras depend so it can not be imported globally.

issue11732
review418511003

account.py

@@ -5,7 +5,6 @@ from decimal import Decimal
 from trytond.i18n import gettext
 from trytond.model import ModelSQL, fields
 from trytond.modules.account.exceptions import AccountMissing
-from trytond.modules.account_invoice.exceptions import PaymentTermComputeError
 from trytond.modules.company.model import CompanyValueMixin
 from trytond.pool import Pool, PoolMeta
 from trytond.pyson import Eval
@@ -130,6 +129,8 @@ class Invoice(metaclass=PoolMeta):
         'payment_term_date')
     def _cash_round_total_amount(self, amount):
         "Round total amount according to cash rounding"
+        from trytond.modules.account_invoice.exceptions import (
+            PaymentTermComputeError)
         pool = Pool()
         Date = pool.get('ir.date')
         if self.currency:

purchase.py

@@ -1,7 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 from trytond.model import fields
-from trytond.modules.account_invoice.exceptions import PaymentTermComputeError
 from trytond.pool import Pool, PoolMeta
 from trytond.pyson import Eval
 from trytond.transaction import Transaction
@@ -55,6 +54,8 @@ class Purchase(metaclass=PoolMeta):
 
     @fields.depends('currency', 'payment_term', 'company')
     def _cash_round_total_amount(self, amount):
+        from trytond.modules.account_invoice.exceptions import (
+            PaymentTermComputeError)
         pool = Pool()
         Date = pool.get('ir.date')
         if self.currency:

sale.py

@@ -1,7 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 from trytond.model import fields
-from trytond.modules.account_invoice.exceptions import PaymentTermComputeError
 from trytond.pool import Pool, PoolMeta
 from trytond.transaction import Transaction
 
@@ -39,6 +38,8 @@ class Sale(metaclass=PoolMeta):
 
     @fields.depends('currency', 'payment_term', 'company')
     def _cash_round_total_amount(self, amount):
+        from trytond.modules.account_invoice.exceptions import (
+            PaymentTermComputeError)
         pool = Pool()
         Date = pool.get('ir.date')
         if self.currency: