Adapt legacy set_switch_state() output typing

Author: bouwew

plugwise/legacy/smile.py

@@ -223,15 +223,15 @@ async def set_schedule_state(
 
     async def set_switch_state(
         self, appl_id: str, members: list[str] | None, model: str, state: str
-    ) -> bool:
+    ) -> bool | None:
         """Set the given state of the relevant switch.
 
         For individual switches, sets the state directly.
         For group switches, sets the state for each member in the group separately.
         For switch-locks, sets the lock state using a different data format.
         Return the requested state when successful, the current state otherwise.
         """
-        current_state = self.gw_entities[appl_id]["switches"]["relay"]
+        current_state = self.gw_entities[appl_id]["switches"].get("relay")
         requested_state = state == STATE_ON
         switch = Munch()
         switch.actuator = "actuator_functionalities"