I have created a problem while trying to get the google calendar api to work, now when I select General Settings > Calendar > API Credentials it get a server error

Can someone shed any light on this error please?

Much appreciated!

Error:
Odoo Server Error

Traceback (most recent call last):
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 650, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 310, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/tools/pycompat.py", line 87, in reraise
    raise value
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 692, in dispatch
    result = self._call_function(**self.params)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 342, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/service/model.py", line 97, in wrapper
    return f(dbname, *args, **kwargs)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 335, in checked_call
    result = self.endpoint(*a, **kw)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 936, in __call__
    return self.method(*args, **kw)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/http.py", line 515, in response_wrap
    response = f(*args, **kw)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/web/controllers/main.py", line 931, in call_kw
    return self._call_kw(model, method, args, kwargs)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/web/controllers/main.py", line 923, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/api.py", line 687, in call_kw
    return call_kw_model(method, model, args, kwargs)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/api.py", line 672, in call_kw_model
    result = method(recs, *args, **kwargs)
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/base/res/res_config.py", line 499, in default_get
    res.update(self.get_values())
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/sale/models/res_config_settings.py", line 137, in get_values
    res = super(ResConfigSettings, self).get_values()
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/website/models/res_config_settings.py", line 71, in get_values
    res = super(ResConfigSettings, self).get_values()
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/google_calendar/models/res_config_settings.py", line 22, in get_values
    res = super(ResConfigSettings, self).get_values()
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/crm/models/res_config_settings.py", line 40, in get_values
    res = super(ResConfigSettings, self).get_values()
  File "/opt/bitnami/apps/odoo/lib/odoo-11.0.post20180518-py3.6.egg/odoo/addons/auth_oauth/models/res_config_settings.py", line 27, in get_values
    auth_oauth_google_enabled=google_provider.enabled,
AttributeError: 'NoneType' object has no attribute 'enabled'