Update led brightness select state only if valid data is available, Xiaomi Miio integration (#57197)

* Update state if there is valid data

* Add comment

homeassistant/components/xiaomi_miio/select.py

@@ -146,10 +146,14 @@ class XiaomiAirHumidifierSelector(XiaomiSelector):
     @callback
     def _handle_coordinator_update(self):
         """Fetch state from the device."""
-        self._current_led_brightness = self._extract_value_from_attribute(
+        led_brightness = self._extract_value_from_attribute(
             self.coordinator.data, self.entity_description.key
         )
-        self.async_write_ha_state()
+        # Sometimes (quite rarely) the device returns None as the LED brightness so we
+        # check that the value is not None before updating the state.
+        if led_brightness:
+            self._current_led_brightness = led_brightness
+            self.async_write_ha_state()
 
     @property
     def current_option(self):