[IMP] models, fields: initialize cache to None for related fields

This makes sense because in `create` the "previous" value of a field is
obviously non-existent.

This avoids having to fetch pre-existing attachments when they are known to be
inexistent, which optimizes stored related binary that are computed post-insert.

odoo/fields.py

@@ -1948,15 +1948,21 @@ class Binary(Field):
         records = cache.get_records_different_from(records, self, cache_value)
         if not records:
             return records
+        if self.store:
+            # determine records that are known to be not null
+            not_null = cache.get_records_different_from(records, self, None)
+
         cache.update(records, self, [cache_value] * len(records))
 
         # retrieve the attachments that store the values, and adapt them
         if self.store:
-            atts = records.env['ir.attachment'].sudo().search([
-                ('res_model', '=', self.model_name),
-                ('res_field', '=', self.name),
-                ('res_id', 'in', records.ids),
-            ])
+            atts = records.env['ir.attachment'].sudo()
+            if not_null:
+                atts = atts.search([
+                    ('res_model', '=', self.model_name),
+                    ('res_field', '=', self.name),
+                    ('res_id', 'in', records.ids),
+                ])
             if value:
                 # update the existing attachments
                 atts.write({'datas': value})

odoo/models.py

@@ -3726,6 +3726,8 @@ Record ids: %(records)s
             for field in self._fields.values():
                 if field.type in ('one2many', 'many2many'):
                     self.env.cache.set(record, field, ())
+                elif field.related and not field.column_type:
+                    self.env.cache.set(record, field, field.convert_to_cache(None, record))
                 # DLE P123: `test_adv_activity`, `test_message_assignation_inbox`, `test_message_log`, `test_create_mail_simple`, ...
                 # Set `mail.message.parent_id` to False in cache so it doesn't do the useless SELECT when computing the modified of `child_ids`
                 # in other words, if `parent_id` is not set, no other message `child_ids` are impacted.