Missing required for field postal_code on country.postal_codes

Not through the interface as there is no view, but with code it's possible to create a record on country.postal_code without the field postal_code.

On loading parties this error raises:

Traceback (most recent call last):
  File "/trytond/wsgi.py", line 109, in dispatch_request
    return endpoint(request, **request.view_args)
  File "/trytond/protocols/dispatcher.py", line 43, in rpc
    return methods.get(request.rpc_method, _dispatch)(
  File "/trytond/wsgi.py", line 75, in wrapper
    return func(request, *args, **kwargs)
  File "/trytond/protocols/wrappers.py", line 200, in wrapper
    return func(request, pool, *args, **kwargs)
  File "/trytond/protocols/dispatcher.py", line 201, in _dispatch
    result = rpc.result(meth(inst, *c_args, **c_kwargs))
  File "/trytond/model/fields/field.py", line 124, in wrapper
    return func(self, *args, **kwargs)
  File "/trytond/modules/party/address.py", line 130, in autocomplete_postal_code
    return self._autocomplete_search(domain, 'postal_code')
  File "/trytond/modules/party/address.py", line 122, in _autocomplete_search
    return sorted({getattr(z, name) for z in records})
TypeError: '<' not supported between instances of 'NoneType' and 'str'

Fault: '<' not supported between instances of 'NoneType' and 'str'