Fix NWS error with no observation (#92997)

Co-authored-by: epenet <6771947+epenet@users.noreply.github.com>

homeassistant/components/nws/sensor.py

@@ -195,9 +195,12 @@ class NWSSensor(CoordinatorEntity[NwsDataUpdateCoordinator], SensorEntity):
     @property
     def native_value(self) -> float | None:
         """Return the state."""
-        value = self._nws.observation.get(self.entity_description.key)
-        if value is None:
+        if (
+            not (observation := self._nws.observation)
+            or (value := observation.get(self.entity_description.key)) is None
+        ):
             return None
+
         # Set alias to unit property -> prevent unnecessary hasattr calls
         unit_of_measurement = self.native_unit_of_measurement
         if unit_of_measurement == UnitOfSpeed.MILES_PER_HOUR:

tests/components/nws/test_sensor.py

@@ -70,10 +70,13 @@ async def test_imperial_metric(
         assert state.attributes.get(ATTR_ATTRIBUTION) == ATTRIBUTION
 
 
-async def test_none_values(hass: HomeAssistant, mock_simple_nws, no_weather) -> None:
+@pytest.mark.parametrize("values", [NONE_OBSERVATION, None])
+async def test_none_values(
+    hass: HomeAssistant, mock_simple_nws, no_weather, values
+) -> None:
     """Test with no values."""
     instance = mock_simple_nws.return_value
-    instance.observation = NONE_OBSERVATION
+    instance.observation = values
 
     registry = er.async_get(hass)