Hello, I usually manage to get by, just using the search but I'm a bit stumped this time. I would appreciate some pointers in to the right direction.

Recently, I've been made aware of crashing/errors occurring during the following:
1. Updating the country field in Contacts, when the contact had no prior entry in the country field.
It crashes on save and produces the following stack trace.

Trace: 
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 1971, in _serve_db
    return service_model.retrying(self._serve_ir_http, self.env)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/service/model.py", line 154, in retrying
    env.cr.flush()  # submit the changes to the database
    ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/sql_db.py", line 138, in flush
    self.precommit.run()
  File "/usr/lib/python3/dist-packages/odoo/tools/misc.py", line 1227, in run
    func()
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_thread.py", line 530, in _track_finalize
    tracking = records.with_context(context)._message_track(fnames, initial_values)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_thread.py", line 612, in _message_track
    tracking[record.id] = record._mail_track(tracked_fields, initial_values_dict[record.id])
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/models.py", line 154, in _mail_track
    [0, 0, self.env['mail.tracking.value']._create_tracking_values(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_tracking_value.py", line 93, in _create_tracking_values
    'new_value_char': new_value and dict(col_info['selection'])[new_value] or ''
                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
KeyError: '0218'

The above server error caused the following client error:
RPC_ERROR: Odoo Server Error

2. When changing the stage of a CRM lead.

Stack trace:
RPC_ERROR
Odoo Server Error
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 1971, in _serve_db
    return service_model.retrying(self._serve_ir_http, self.env)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/service/model.py", line 154, in retrying
    env.cr.flush()  # submit the changes to the database
    ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/sql_db.py", line 138, in flush
    self.precommit.run()
  File "/usr/lib/python3/dist-packages/odoo/tools/misc.py", line 1227, in run
    func()
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_thread.py", line 530, in _track_finalize
    tracking = records.with_context(context)._message_track(fnames, initial_values)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_thread.py", line 636, in _message_track
    record.message_post(
  File "/usr/lib/python3/dist-packages/odoo/addons/sms/models/mail_thread.py", line 52, in message_post
    return super().message_post(*args, body=body, message_type=message_type, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/rating/models/mail_thread.py", line 178, in message_post
    message = super(MailThread, self).message_post(**kwargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_thread.py", line 2223, in message_post
    new_message = self._message_create([msg_values])
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/rating/models/mail_thread.py", line 34, in _message_create
    return super()._message_create(values_list)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_thread.py", line 2912, in _message_create
    ).create(create_values_list)
      ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<decorator-gen-61>", line 2, in create
  File "/usr/lib/python3/dist-packages/odoo/api.py", line 431, in _model_create_multi
    return create(self, arg)
           ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_message.py", line 687, in create
    vals_lst = [dict(cmd[2], mail_message_id=message.id) for cmd in tracking_values_cmd if len(cmd) == 3 and cmd[0] == 0]
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/odoo/addons/mail/models/mail_message.py", line 687, in <listcomp>
    vals_lst = [dict(cmd[2], mail_message_id=message.id) for cmd in tracking_values_cmd if len(cmd) == 3 and cmd[0] == 0]
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable
 
The above server error caused the following client error:
RPC_ERROR: Odoo Server Error

3. (Speculation) I suspect that there is some common root cause and there might be other occasions, where it might result in crashing.

It seems that the common theme is "tracking values", but I'm not sure where I should be looking in to next.

Thanks for reading, any help would be greatly appreciated.