Allow null / None value for non numeric mqtt sensor without warnings (#127032)

Allow `null` / `None` value for mqtt sensor without warnings

homeassistant/components/mqtt/sensor.py

@@ -260,14 +260,18 @@ class MqttSensor(MqttEntity, RestoreSensor):
                 msg.topic,
             )
             return
+
+        if payload == PAYLOAD_NONE:
+            self._attr_native_value = None
+            return
+
         if self._numeric_state_expected:
             if payload == "":
                 _LOGGER.debug("Ignore empty state from '%s'", msg.topic)
-            elif payload == PAYLOAD_NONE:
-                self._attr_native_value = None
             else:
                 self._attr_native_value = payload
             return
+
         if self.options and payload not in self.options:
             _LOGGER.warning(
                 "Ignoring invalid option received on topic '%s', got '%s', allowed: %s",

tests/components/mqtt/test_sensor.py

@@ -299,6 +299,17 @@ async def test_setting_sensor_to_long_state_via_mqtt_message(
             STATE_UNKNOWN,
             True,
         ),
+        (
+            help_custom_config(
+                sensor.DOMAIN,
+                DEFAULT_CONFIG,
+                ({"device_class": sensor.SensorDeviceClass.TIMESTAMP},),
+            ),
+            sensor.SensorDeviceClass.TIMESTAMP,
+            "None",
+            STATE_UNKNOWN,
+            False,
+        ),
         (
             help_custom_config(
                 sensor.DOMAIN,