Fix handling None or empty value for numeric MQTT sensor (#87004)

* Allow `None` for numeric sensor, ignore empty val

* Add test case with omitting a value

* Use _numeric_state_expected property

* Only respect None if numeric state is expected

homeassistant/components/mqtt/sensor.py

@@ -38,7 +38,7 @@ from homeassistant.util import dt as dt_util
 
 from . import subscription
 from .config import MQTT_RO_SCHEMA
-from .const import CONF_ENCODING, CONF_QOS, CONF_STATE_TOPIC
+from .const import CONF_ENCODING, CONF_QOS, CONF_STATE_TOPIC, PAYLOAD_NONE
 from .debug_info import log_messages
 from .mixins import (
     MQTT_ENTITY_COMMON_SCHEMA,
@@ -272,13 +272,19 @@ class MqttSensor(MqttEntity, RestoreSensor):
             payload = self._template(msg.payload, PayloadSentinel.DEFAULT)
             if payload is PayloadSentinel.DEFAULT:
                 return
-            if self.device_class not in {
-                SensorDeviceClass.DATE,
-                SensorDeviceClass.TIMESTAMP,
-            }:
-                self._attr_native_value = str(payload)
+            new_value = str(payload)
+            if self._numeric_state_expected:
+                if new_value == "":
+                    _LOGGER.debug("Ignore empty state from '%s'", msg.topic)
+                elif new_value == PAYLOAD_NONE:
+                    self._attr_native_value = None
+                else:
+                    self._attr_native_value = new_value
                 return
-            if (payload_datetime := dt_util.parse_datetime(str(payload))) is None:
+            if self.device_class is None:
+                self._attr_native_value = new_value
+                return
+            if (payload_datetime := dt_util.parse_datetime(new_value)) is None:
                 _LOGGER.warning(
                     "Invalid state message '%s' from '%s'", msg.payload, msg.topic
                 )

tests/components/mqtt/test_sensor.py

@@ -169,6 +169,61 @@ async def test_setting_sensor_native_value_handling_via_mqtt_message(
     assert log == ("Invalid state message" in caplog.text)
 
 
+async def test_setting_numeric_sensor_native_value_handling_via_mqtt_message(
+    hass: ha.HomeAssistant,
+    mqtt_mock_entry_with_yaml_config,
+) -> None:
+    """Test the setting of a numeric sensor value via MQTT."""
+    assert await async_setup_component(
+        hass,
+        mqtt.DOMAIN,
+        {
+            mqtt.DOMAIN: {
+                sensor.DOMAIN: {
+                    "name": "test",
+                    "state_topic": "test-topic",
+                    "value_template": "{{ value_json.power }}",
+                    "device_class": "power",
+                    "unit_of_measurement": "W",
+                }
+            }
+        },
+    )
+    await hass.async_block_till_done()
+    await mqtt_mock_entry_with_yaml_config()
+
+    # float value
+    async_fire_mqtt_message(hass, "test-topic", '{ "power": 45.3, "current": 5.24 }')
+    state = hass.states.get("sensor.test")
+    assert state.attributes.get("device_class") == "power"
+    assert state.state == "45.3"
+
+    # null value, native value should be None
+    async_fire_mqtt_message(hass, "test-topic", '{ "power": null, "current": 5.34 }')
+    state = hass.states.get("sensor.test")
+    assert state.state == "unknown"
+
+    # int value
+    async_fire_mqtt_message(hass, "test-topic", '{ "power": 20, "current": 5.34 }')
+    state = hass.states.get("sensor.test")
+    assert state.state == "20"
+
+    # int value
+    async_fire_mqtt_message(hass, "test-topic", '{ "power": "21", "current": 5.34 }')
+    state = hass.states.get("sensor.test")
+    assert state.state == "21"
+
+    # ignore empty value, native sensor value should not change
+    async_fire_mqtt_message(hass, "test-topic", '{ "power": "", "current": 5.34 }')
+    state = hass.states.get("sensor.test")
+    assert state.state == "21"
+
+    # omitting value, causing it to be ignored, native sensor value should not change (template warning will be logged though)
+    async_fire_mqtt_message(hass, "test-topic", '{ "current": 5.34 }')
+    state = hass.states.get("sensor.test")
+    assert state.state == "21"
+
+
 async def test_setting_sensor_value_expires_availability_topic(
     hass, mqtt_mock_entry_with_yaml_config, caplog
 ):