Erro ao cadastrar uma fatura de Cliente

Ao cadastrar uma fatura de Cliente, o sistema apresenta uma mensagem de erro quando o usuário seleciona o produto:

OpenERP Server Error
Client Traceback (most recent call last):
  File "/opt/openerp/web/addons/web/http.py", line 204, in dispatch
    response["result"] = method(self, **self.params)
  File "/opt/openerp/web/addons/web/controllers/main.py", line 1128, in call_kw
    return self._call_kw(req, model, method, args, kwargs)
  File "/opt/openerp/web/addons/web/controllers/main.py", line 1120, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/opt/openerp/web/addons/web/session.py", line 42, in proxy
    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)
  File "/opt/openerp/web/addons/web/session.py", line 30, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/opt/openerp/web/addons/web/session.py", line 103, in send
    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)

Server Traceback (most recent call last):
  File "/opt/openerp/web/addons/web/session.py", line 89, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/opt/openerp/server/openerp/netsvc.py", line 296, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/opt/openerp/server/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/opt/openerp/server/openerp/osv/osv.py", line 190, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/opt/openerp/server/openerp/osv/osv.py", line 132, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/opt/openerp/server/openerp/osv/osv.py", line 199, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/opt/openerp/server/openerp/osv/osv.py", line 187, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/opt/openerp/addons/account/account_invoice.py", line 1543, in uos_id_change
    res = self.product_id_change(cr, uid, ids, product, uom, qty, name, type, partner_id, fposition_id, price_unit, currency_id, context=context)
  File "/opt/openerp/addons/account_analytic_plans/account_analytic_plans.py", line 312, in product_id_change
    res_prod = super(account_invoice_line, self).product_id_change(cr, uid, ids, product, uom_id, qty, name, type, partner_id, fposition_id, price_unit, currency_id, context=context, company_id=company_id)
  File "/opt/openerp/localizacao_br/l10n_br_account/account_invoice.py", line 2323, in product_id_change
    fiscal_data = self._fiscal_position_map(cr, uid, ids, partner_id, company_id, fiscal_operation_category_id)
  File "/opt/openerp/localizacao_br/l10n_br_account/account_invoice.py", line 2294, in _fiscal_position_map
    fiscal_result = obj_rule.fiscal_position_map(cr, uid, partner_id, company_id, fiscal_operation_category_id, context={'use_domain': ('use_invoice','=',True)})
  File "/opt/openerp/localizacao_br/l10n_br_account/account_fiscal_position_rule.py", line 92, in fiscal_position_map
    from_country = obj_company.partner_id.country_id.id
AttributeError: 'NoneType' object has no attribute 'country_id'