core: Mystrom integration is broken in 0.108

The problem

I just updated from 0.107.7 to 0.108.0 and all my mystrom switches are no longer available. Homeassistant complains about a key error.

Environment

• Home Assistant Core release with the issue: 0.108.0
• Last working Home Assistant Core release (if known): 0.107.7
• Operating environment (Home Assistant/Supervised/Docker/venv): Not sure, it is running on a Ubuntu 18.04 server edition, but there the supervised version is installed which uses docker…
• Integration causing this issue: mystrom
• Link to integration documentation on our website: https://www.home-assistant.io/integrations/mystrom/

Problem-relevant configuration.yaml

switch:
    - platform: mystrom
      host: 192.168.4.20
      name: Fernseher Schlafzimmer
    - platform: mystrom
      host: 192.168.4.21
      name: MyStrom Sonos Kueche
    - platform: mystrom
      host: 192.168.4.22
      name: MyStrom Sonos Schlafzimmer
    - platform: mystrom
      host: 192.168.4.23
      name: MyStrom Sonos Buero
    - platform: mystrom
      host: 192.168.4.24
      name: MyStrom Sonos One Wohnzimmer
    - platform: mystrom
      host: 192.168.4.25
      name: MyStrom Sonos Beam Wohnzimmer
    - platform: mystrom
      host: 192.168.4.26
      name: MyStrom Phone Charger
    - platform: mystrom
      host: 192.168.4.27
      name: MyStrom Aquarium Licht
    - platform: mystrom
      host: 192.168.4.28
      name: MyStrom Aquarium Heizung
    - platform: mystrom
      host: 192.168.4.29
      name: MyStrom Aquarium Filter
    - platform: mystrom
      host: 192.168.4.30
      name: MyStrom Aquarium Luftpumpe
    - platform: mystrom
      host: 192.168.4.31
      name: MyStrom Aquarium Ventilator

Traceback/Error logs

2020-04-08 20:51:04 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/entity_platform.py", line 295, in async_add_entities
    await asyncio.gather(*tasks)
  File "/usr/src/homeassistant/homeassistant/helpers/entity_platform.py", line 447, in _async_add_entity
    await entity.async_update_ha_state()
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 284, in async_update_ha_state
    self._async_write_ha_state()
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 320, in _async_write_ha_state
    state = self.state
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 612, in state
    return STATE_ON if self.is_on else STATE_OFF
  File "/usr/src/homeassistant/homeassistant/components/mystrom/switch.py", line 60, in is_on
    return bool(self.data["relay"])
KeyError: 'relay'

Additional information