Arreglar campo en modulo de Odoo

Hay que arreglar un modulo de Nominas de pago para Chile modificado por un programador que lo dejo funcionando mal. Seguramente es una herencia o algo por el estilo. Abajo el error. Es algo rapido de solucionar.

Odoo Server Error
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/odoo/addons/base/models/ir_http.py", line 237, in _dispatch
result = request.dispatch()
File "/usr/lib/python3/dist-packages/odoo/http.py", line 684, in dispatch
result = self._call_function(**self.params)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 360, in _call_function
return checked_call(self.db, *args, **kwargs)
File "/usr/lib/python3/dist-packages/odoo/service/model.py", line 94, in wrapper
return f(dbname, *args, **kwargs)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 348, in checked_call
result = self.endpoint(*a, **kw)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 913, in __call__
return self.method(*args, **kw)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 532, in response_wrap
response = f(*args, **kw)
File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1396, in call_button
action = self._call_kw(model, method, args, kwargs)
File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1384, in _call_kw
return call_kw(request.env[model], method, args, kwargs)
File "/usr/lib/python3/dist-packages/odoo/api.py", line 399, in call_kw
result = _call_kw_multi(method, model, args, kwargs)
File "/usr/lib/python3/dist-packages/odoo/api.py", line 386, in _call_kw_multi
result = method(recs, *args, **kwargs)
File "/mnt/extra-addons/payroll_suppliers/models/payroll_invoice.py", line 102, in save_excel
self.export_excel()
File "/mnt/extra-addons/payroll_suppliers/models/payroll_invoice.py", line 163, in export_excel
rut = invoice.partner_id.vat
Exception

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

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/odoo/http.py", line 640, in _handle_exception
return super(JsonRequest, self)._handle_exception(exception)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 316, in _handle_exception
raise exception.with_traceback(None) from new_cause
AttributeError: 'payroll.invoice.factura' object has no attribute 'partner_id'