Hi, we get AttributeError when pressing a button to change the state of an RFQ in our Odoo system while running this function:

def state_machine_trigger(self, trigger_name):
self.ensure_one()
proxy = Proxy(self, "state")
MACHINE.add_model(proxy, initial=self.state)
try:
proxy.trigger(trigger_name)
except MachineError as e:
_LOGGER.exception(e)
except Exception:
_LOGGER.exception("here be bork")
finally:
MACHINE.remove_model(proxy)

Traceback (most recent call last):
File "/home/odoo/odoo/lib/odoo/odoo/addons/base/models/ir_http.py", line 237, in _dispatch
result = request.dispatch()
File "/home/odoo/odoo/lib/odoo/odoo/http.py", line 685, in dispatch
result = self._call_function(**self.params)
File "/home/odoo/odoo/lib/odoo/odoo/http.py", line 361, in _call_function
return checked_call(self.db, *args, **kwargs)
File "/home/odoo/odoo/lib/odoo/odoo/service/model.py", line 94, in wrapper
return f(dbname, *args, **kwargs)
File "/home/odoo/odoo/lib/odoo/odoo/http.py", line 357, in checked_call
self._cr.precommit.run()
File "/home/odoo/odoo/lib/odoo/odoo/tools/misc.py", line 1165, in run
func()
File "/home/odoo/odoo/lib/odoo/addons/mail/models/mail_thread.py", line 550, in _finalize_tracking
tracking = records.with_context(context).message_track(fnames, initial_values)
File "/home/odoo/odoo/lib/odoo/addons/mail/models/mail_thread.py", line 626, in message_track
if not subtype.exists():
Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/home/odoo/odoo/lib/odoo/odoo/http.py", line 641, in _handle_exception
return super(JsonRequest, self)._handle_exception(exception)
File "/home/odoo/odoo/lib/odoo/odoo/http.py", line 317, in _handle_exception
raise exception.with_traceback(None) from new_cause
AttributeError: 'str' object has no attribute 'exists'