AttributeError: '' Model has no attribute '_changed_values'

Hello everyone,
It was develop a module (party_ruc_pe) which adds the identifiers fields (Tipo documento, Codigo documento) to party form view in order to get some data like name, address and add a record to Identifiers tab as shown on the next picture:

In version 4.2 it works fine, but now that it has been upgraded to version 5.0 the following error is thrown:

Traceback (most recent call last):
  File "/trytond/model/", line 396, in __getattr__
    return self._values[name]
KeyError: '_changed_values'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/trytond/", line 73, in dispatch_request
    return endpoint(request, **request.view_args)
  File "/trytond/protocols/", line 46, in rpc
    request, database_name, *request.rpc_params)
  File "/trytond/", line 44, in auth_required
    return wrapped(*args, **kwargs)
  File "/trytond/protocols/", line 122, in wrapper
    return func(request, pool, *args, **kwargs)
  File "/trytond/protocols/", line 181, in _dispatch
    result = rpc.result(meth(inst, *c_args, **c_kwargs))
  File "/trytond/model/", line 709, in on_change
    return [self._changed_values]
  File "/trytond/model/", line 1281, in __getattr__
    return super(ModelStorage, self).__getattr__(name)
  File "/trytond/model/", line 399, in __getattr__
    % (self.__name__, name, self._values))
AttributeError: '' Model has no attribute '_changed_values': {'document_code': '10762992979', 'name': 'ROMERO ALMONTE YOEL DIOMEDEZ', 'type': 'pe_vat', 'addresses': (Pool().get('party.address')(**{'active': True, 'city': '', 'country': 176, 'delivery': False, 'district': 6356, 'google_maps_url': '', 'invoice': True, 'name': '', 'party_name': '', 'province': 4963, 'sequence': None, 'street': '', 'subdivision': 2223, 'ubigeo': '150101', 'zip': ''}),), 'identifiers': (Pool().get('party.identifier')(**{'party': -1, 'code': '10762992979', 'type': 'pe_vat'}),), 'message': 'Documento válido'}

So, debugging the module, it was found that the code line that causes the error is: self.identifiers = tuple(aux_identifiers) and this line is the one that adds the record to Identifiers tab. And well, I was wondering:

  • if there’s a way to rewrite that line to make it work in version 5.0 and how would it be?
  • Why this happens, though?

Normally it should work but it seems there is an attribute error when calling ModeView._changed_values. The property decorator hide this exception but to be able to understand what is happening, we will need the traceback of this exception.