[FIX] base: fix merge partner wizard

In the contacts app, you can select 2 partners and merge them.

Before this commit:

    - If a partner was added by a SQL query and not directly on Odoo,
      the create_date will be empty. This causes a crash because the
      merge wizard try to sort the partners by date

After this commit:

    - If a partner do not have a create_date, it will be considered
      as 01/01/1970. The merge wizard will sort the partners by IDs too.

OPW-2091925

closes odoo/odoo#39503

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

odoo/addons/base/wizard/base_partner_merge.py

@@ -6,6 +6,7 @@ import functools
 import itertools
 import logging
 import psycopg2
+import datetime
 
 from odoo import api, fields, models
 from odoo import SUPERUSER_ID, _
@@ -390,11 +391,11 @@ class MergePartnerAutomatic(models.TransientModel):
 
     @api.model
     def _get_ordered_partner(self, partner_ids):
-        """ Helper : returns a `res.partner` recordset ordered by create_date/active fields
+        """ Helper : returns a `res.partner` recordset ordered by id/create_date/active fields
             :param partner_ids : list of partner ids to sort
         """
         return self.env['res.partner'].browse(partner_ids).sorted(
-            key=lambda p: (p.active, (p.create_date or '')),
+            key=lambda p: (p.active, (p.create_date or datetime.datetime(1970, 1, 1), p.id)),
             reverse=True,
         )