[FIX] sale: ensure a non null date

Sometimes, a sale.order in the SALE state doesn't have a confirmed date,
which can cause a traceback. To avoid this, when confirmation_date is
null, use the write_date, which is never NULL when sale.order is in sale
state.
In migration, we will try to populate the confirmation date with
the mail.message subtype. As ultimate fallback, we will take
the write_date.

closes odoo/odoo#28296

addons/sale/models/sale.py

@@ -228,7 +228,7 @@ class SaleOrder(models.Model):
         """
         for order in self:
             dates_list = []
-            confirm_date = fields.Datetime.from_string(order.confirmation_date if order.state == 'sale' else fields.Datetime.now())
+            confirm_date = fields.Datetime.from_string((order.confirmation_date or order.write_date) if order.state == 'sale' else fields.Datetime.now())
             for line in order.order_line.filtered(lambda x: x.state != 'cancel' and not x._is_delivery()):
                 dt = confirm_date + timedelta(days=line.customer_lead or 0.0)
                 dates_list.append(dt)

addons/sale_stock/models/sale_order.py

@@ -48,7 +48,7 @@ class SaleOrder(models.Model):
         super(SaleOrder, self)._compute_expected_date()
         for order in self:
             dates_list = []
-            confirm_date = fields.Datetime.from_string(order.confirmation_date if order.state == 'sale' else fields.Datetime.now())
+            confirm_date = fields.Datetime.from_string((order.confirmation_date or order.write_date) if order.state == 'sale' else fields.Datetime.now())
             for line in order.order_line.filtered(lambda x: x.state != 'cancel' and not x._is_delivery()):
                 dt = confirm_date + timedelta(days=line.customer_lead or 0.0)
                 dates_list.append(dt)