[FIX] account: reversal has no partner id

Current behaviour:
When reversing a bank statement,
the partner id gets removed

Steps to reproduce:
1. Go to Accounting, Journal Entries
2. Select/Create a bank statement with partner
3. Click on Reverse entry, then Reverse
4. Head back to Journal Entries
5. Reversal of the bank statement has no partner

opw-3345594

closes odoo/odoo#126992

X-original-commit: 72d82ed813c4baa11060ebcd1df6335410c5e337
Signed-off-by: William André (wan) <wan@odoo.com>

addons/account/models/account_move.py

@@ -2249,6 +2249,9 @@ class AccountMove(models.Model):
                     if command == Command.CREATE
                     and line_vals.get('display_type') not in ('payment_term', 'tax', 'rounding')
                 ]
+            elif move.move_type == 'entry':
+                if 'partner_id' not in data:
+                    data['partner_id'] = False
         if not self.journal_id.active and 'journal_id' in data_list:
             del default['journal_id']
         return data_list
@@ -2258,8 +2261,6 @@ class AccountMove(models.Model):
         default = dict(default or {})
         if (fields.Date.to_date(default.get('date')) or self.date) <= self.company_id._get_user_fiscal_lock_date():
             default['date'] = self.company_id._get_user_fiscal_lock_date() + timedelta(days=1)
-        if self.move_type == 'entry':
-            default['partner_id'] = False
         copied_am = super().copy(default)
         message_origin = '' if not copied_am.auto_post_origin_id else \
             (Markup('<br/>') + _('This recurring entry originated from %s')) % copied_am.auto_post_origin_id._get_html_link()
@@ -3437,6 +3438,7 @@ class AccountMove(models.Model):
             default_values.update({
                 'move_type': TYPE_REVERSE_MAP[move.move_type],
                 'reversed_entry_id': move.id,
+                'partner_id': move.partner_id.id,
             })
             reverse_moves += move.with_context(
                 move_reverse_cancel=cancel,

addons/account/tests/test_account_bank_statement.py

@@ -1424,3 +1424,26 @@ class TestAccountBankStatementLine(AccountTestInvoicingCommon):
             {'res_id': statement.id, 'res_model': 'account.bank.statement'},
             {'res_id': statement.id, 'res_model': 'account.bank.statement'},
         ])
+
+    def test_statement_reverse_keeps_partner(self):
+        partner = self.env['res.partner'].create({
+            'name': 'Test Partner',
+        })
+
+        statement_line = self.env['account.bank.statement.line'].create({
+            'date': '2019-01-01',
+            'payment_ref': 'line_1',
+            'partner_id': partner.id,
+            'journal_id': self.bank_journal_1.id,
+            'amount': 1250.0,
+        })
+        move = statement_line.move_id
+
+        move_reversal = self.env['account.move.reversal'].with_context(active_model="account.move", active_ids=move.ids).create({
+            'date': fields.Date.from_string('2021-02-01'),
+            'journal_id': self.bank_journal_1.id,
+        })
+        reversal = move_reversal.reverse_moves()
+        reversed_move = self.env['account.move'].browse(reversal['res_id'])
+
+        self.assertEqual(reversed_move.partner_id, partner)