FIX exception when power is not retrieved at first run

custom_components/versatile_thermostat/climate.py

@@ -810,7 +810,9 @@ class VersatileThermostat(ClimateEntity, RestoreEntity):
         _LOGGER.debug(event)
         new_state = event.data.get("new_state")
         old_state = event.data.get("old_state")
-        if new_state is None or new_state.state == old_state.state:
+        if new_state is None or (
+            old_state is not None and new_state.state == old_state.state
+        ):
             return
 
         try: