[FIX] product_expiry: default expiration_date

Before this commit, the default `expiration_date` wasn't set when the
move line was created with the help of multiple assign serial numbers
button or when user wrote/copy-pasted a list of SN/LN.

task-2166230

closes odoo/odoo#42809

X-original-commit: ff6126e8077031fb20eada5f3f9d8fd8a4a4c56a
Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/product_expiry/models/stock_move.py

 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
+import datetime
+
 from odoo import fields, models
 
 
@@ -8,3 +10,13 @@ class StockMove(models.Model):
     _inherit = "stock.move"
     use_expiration_date = fields.Boolean(
         string='Use Expiration Date', related='product_id.use_expiration_date')
+
+    def _generate_serial_move_line_commands(self, lot_names, origin_move_line=None):
+        """Override to add a default `expiration_date` into the move lines values."""
+        move_lines_commands = super()._generate_serial_move_line_commands(lot_names, origin_move_line=origin_move_line)
+        if self.product_id.use_expiration_date:
+            date = fields.Datetime.today() + datetime.timedelta(days=self.product_id.expiration_time)
+            for move_line_command in move_lines_commands:
+                move_line_vals = move_line_command[2]
+                move_line_vals['expiration_date'] = date
+        return move_lines_commands