core: Google Calendar integration broken

The problem

Errors since 3pm. The calendar could not be loaded/refreshed

What is version of Home Assistant Core has the issue?

2021.1.4

What was the last working version of Home Assistant Core?

2021.1.4

What type of installation are you running?

Home Assistant OS

Integration causing the issue

Google Calendar

Link to integration documentation on our website

No response

Example YAML snippet

# Put your YAML below this line
google:
  client_id: !secret google_client
  client_secret: !secret google_access


- cal_id: joerg.nauen@gmail.com
  entities:
    - device_id: gmail_urlaub
      ignore_availability: true
      name: joerg.nauen@gmail.com
      search: "Urlaub"
      track: true
      max_results: 50

- cal_id: de.german#holiday@group.v.calendar.google.com
  entities:
    - device_id: feiertage_in_deutschland
      ignore_availability: true
      name: Feiertage in Deutschland
      track: true
      max_results: 20

- cal_id: familieslavescunauen@gmail.com
  entities:
    - device_id: jorg_nauen
      ignore_availability: true
      name: "Joerg Nauen"
      track: true
      max_results: 20

Anything in the logs that might be useful for us?

# Put your logs below this line
Logger: homeassistant.core
Source: components/google/__init__.py:347
First occurred: 17:36:01 (1 occurrences)
Last logged: 17:36:01

Error executing service: <ServiceCall google.scan_for_calendars (c:76d59796e2875789e5db05d5bf80582d)>
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/core.py", line 1461, in catch_exceptions
    await coro_or_task
  File "/usr/src/homeassistant/homeassistant/core.py", line 1484, in _execute_service
    await self._hass.async_add_executor_job(handler.job.target, service_call)
  File "/usr/local/lib/python3.8/concurrent/futures/thread.py", line 57, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/src/homeassistant/homeassistant/components/google/__init__.py", line 257, in _scan_for_calendars
    service = calendar_service.get()
  File "/usr/src/homeassistant/homeassistant/components/google/__init__.py", line 347, in get
    http = credentials.authorize(httplib2.Http())
AttributeError: 'NoneType' object has no attribute 'authorize'


Logger: homeassistant.components.calendar
Source: components/google/__init__.py:347
Integration: Kalender (documentation, issues)
First occurred: 17:36:02 (3 occurrences)
Last logged: 17:36:05

google: Error on device update!
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/entity_platform.py", line 359, in _async_add_entity
    await entity.async_device_update(warning=False)
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 466, in async_device_update
    await task
  File "/usr/local/lib/python3.8/concurrent/futures/thread.py", line 57, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/src/homeassistant/homeassistant/components/google/calendar.py", line 106, in update
    self.data.update()
  File "/usr/src/homeassistant/homeassistant/util/__init__.py", line 239, in wrapper
    result = method(*args, **kwargs)
  File "/usr/src/homeassistant/homeassistant/components/google/calendar.py", line 169, in update
    service, params = self._prepare_query()
  File "/usr/src/homeassistant/homeassistant/components/google/calendar.py", line 132, in _prepare_query
    service = self.calendar_service.get()
  File "/usr/src/homeassistant/homeassistant/components/google/__init__.py", line 347, in get
    http = credentials.authorize(httplib2.Http())
AttributeError: 'NoneType' object has no attribute 'authorize'