Add explicit return none and binary sensor availability to yeelight (#35649)

* Add explicit return none and binary sensor availbility

* Fix

homeassistant/components/yeelight/binary_sensor.py

@@ -47,6 +47,13 @@ class YeelightNightlightModeSensor(BinarySensorEntity):
         if unique:
             return unique + "-nightlight_sensor"
 
+        return None
+
+    @property
+    def available(self) -> bool:
+        """Return if bulb is available."""
+        return self._device.available
+
     @property
     def should_poll(self):
         """No polling needed."""

homeassistant/components/yeelight/light.py

@@ -917,6 +917,8 @@ class YeelightNightLightMode(YeelightGenericLight):
         if unique:
             return unique + "-nightlight"
 
+        return None
+
     @property
     def name(self) -> str:
         """Return the name of the device if any."""