core: Update for sensor.opensky fails

The problem

“Update for sensor.opensky fails” The actual integration never updates, and doesn’t seem to pull any information.

Environment

• Home Assistant Core release with the issue: 0.118.2
• Last working Home Assistant Core release (if known): None
• Operating environment (OS/Container/Supervised/Core): Core
• Integration causing this issue: opensky
• Link to integration documentation on our website: https://www.home-assistant.io/integrations/opensky/

Problem-relevant configuration.yaml

sensor:
  - platform: opensky
    name: OpenSky
    radius: 5.0

Traceback/Error logs

Logger: homeassistant.helpers.entity
Source: components/opensky/sensor.py:135
First occurred: 4:34:35 PM (1 occurrences)
Last logged: 4:34:35 PM
Update for sensor.opensky fails

Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 278, in async_update_ha_state
    await self.async_device_update()
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 474, in async_device_update
    raise exc
  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/opensky/sensor.py", line 135, in update
    states = self._session.get(OPENSKY_API_URL).json().get(ATTR_STATES)
  File "/usr/local/lib/python3.8/site-packages/requests/models.py", line 900, in json
    return complexjson.loads(self.text, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/simplejson/__init__.py", line 525, in loads
    return _default_decoder.decode(s)
  File "/usr/local/lib/python3.8/site-packages/simplejson/decoder.py", line 370, in decode
    obj, end = self.raw_decode(s)
  File "/usr/local/lib/python3.8/site-packages/simplejson/decoder.py", line 400, in raw_decode
    return self.scan_once(s, idx=_w(s, idx).end())
simplejson.errors.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Additional information