When I fill in the VAT field, I receive the following error and the number is not saved. Can somebody help me to get rid of the error to save the VAT numbers of my customers - Thanks!

Fehler:
Odoo Server Error

Traceback (most recent call last):
  File "/opt/odoo/odoo11/odoo/http.py", line 647, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/opt/odoo/odoo11/odoo/http.py", line 307, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/opt/odoo/odoo11/odoo/tools/pycompat.py", line 87, in reraise
    raise value
  File "/opt/odoo/odoo11/odoo/http.py", line 689, in dispatch
    result = self._call_function(**self.params)
  File "/opt/odoo/odoo11/odoo/http.py", line 339, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/opt/odoo/odoo11/odoo/service/model.py", line 97, in wrapper
    return f(dbname, *args, **kwargs)
  File "/opt/odoo/odoo11/odoo/http.py", line 332, in checked_call
    result = self.endpoint(*a, **kw)
  File "/opt/odoo/odoo11/odoo/http.py", line 933, in __call__
    return self.method(*args, **kw)
  File "/opt/odoo/odoo11/odoo/http.py", line 512, in response_wrap
    response = f(*args, **kw)
  File "/opt/odoo/odoo11/addons/web/controllers/main.py", line 930, in call_kw
    return self._call_kw(model, method, args, kwargs)
  File "/opt/odoo/odoo11/addons/web/controllers/main.py", line 922, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/opt/odoo/odoo11/odoo/api.py", line 689, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/opt/odoo/odoo11/odoo/api.py", line 680, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/opt/odoo/odoo11/odoo/models.py", line 5025, in onchange
    record._onchange_eval(name, field_onchange[name], result)
  File "/opt/odoo/odoo11/odoo/models.py", line 4920, in _onchange_eval
    method_res = method(self)
  File "/opt/odoo/odoo11/addons/base_vat_autocomplete/models/res_partner.py", line 52, in vies_vat_change
    if len(partner.vat) > 5 and partner.vat[:2].lower() in stdnum_vat.country_codes:
AttributeError: module 'stdnum.eu.vat' has no attribute 'country_codes'