Do not validate device classes when entity state is unknown (#84860)

homeassistant/components/sensor/__init__.py

@@ -968,6 +968,7 @@ class SensorEntity(Entity):
         # Validate unit of measurement used for sensors with a device class
         if (
             not self._invalid_unit_of_measurement_reported
+            and value is not None
             and device_class
             and (units := DEVICE_CLASS_UNITS.get(device_class)) is not None
             and native_unit_of_measurement not in units

tests/components/sensor/test_init.py

@@ -1144,7 +1144,7 @@ async def test_device_classes_with_invalid_unit_of_measurement(
     platform.init(empty=True)
     platform.ENTITIES["0"] = platform.MockSensor(
         name="Test",
-        native_value=None,
+        native_value="1.0",
         device_class=device_class,
         native_unit_of_measurement="INVALID!",
     )