Fix unbound variable in Group sensor (#87878)

* group bound last

* Add test

homeassistant/components/group/sensor.py

@@ -137,7 +137,7 @@ async def async_setup_entry(
 
 def calc_min(
     sensor_values: list[tuple[str, float, State]]
-) -> tuple[dict[str, str | None], float]:
+) -> tuple[dict[str, str | None], float | None]:
     """Calculate min value."""
     val: float | None = None
     entity_id: str | None = None
@@ -153,7 +153,7 @@ def calc_min(
 
 def calc_max(
     sensor_values: list[tuple[str, float, State]]
-) -> tuple[dict[str, str | None], float]:
+) -> tuple[dict[str, str | None], float | None]:
     """Calculate max value."""
     val: float | None = None
     entity_id: str | None = None
@@ -169,7 +169,7 @@ def calc_max(
 
 def calc_mean(
     sensor_values: list[tuple[str, float, State]]
-) -> tuple[dict[str, str | None], float]:
+) -> tuple[dict[str, str | None], float | None]:
     """Calculate mean value."""
     result = (sensor_value for _, sensor_value, _ in sensor_values)
 
@@ -179,7 +179,7 @@ def calc_mean(
 
 def calc_median(
     sensor_values: list[tuple[str, float, State]]
-) -> tuple[dict[str, str | None], float]:
+) -> tuple[dict[str, str | None], float | None]:
     """Calculate median value."""
     result = (sensor_value for _, sensor_value, _ in sensor_values)
 
@@ -189,10 +189,11 @@ def calc_median(
 
 def calc_last(
     sensor_values: list[tuple[str, float, State]]
-) -> tuple[dict[str, str | None], float]:
+) -> tuple[dict[str, str | None], float | None]:
     """Calculate last value."""
     last_updated: datetime | None = None
     last_entity_id: str | None = None
+    last: float | None = None
     for entity_id, state_f, state in sensor_values:
         if last_updated is None or state.last_updated > last_updated:
             last_updated = state.last_updated
@@ -227,7 +228,9 @@ def calc_sum(
 
 CALC_TYPES: dict[
     str,
-    Callable[[list[tuple[str, float, State]]], tuple[dict[str, str | None], float]],
+    Callable[
+        [list[tuple[str, float, State]]], tuple[dict[str, str | None], float | None]
+    ],
 ] = {
     "min": calc_min,
     "max": calc_max,

tests/components/group/test_sensor.py

@@ -368,3 +368,28 @@ async def test_sensor_calculated_properties(hass: HomeAssistant) -> None:
     assert state.attributes.get("device_class") is None
     assert state.attributes.get("state_class") is None
     assert state.attributes.get("unit_of_measurement") is None
+
+
+async def test_last_sensor(hass: HomeAssistant) -> None:
+    """Test the last sensor."""
+    config = {
+        SENSOR_DOMAIN: {
+            "platform": GROUP_DOMAIN,
+            "name": "test_last",
+            "type": "last",
+            "entities": ["sensor.test_1", "sensor.test_2", "sensor.test_3"],
+            "unique_id": "very_unique_id_last_sensor",
+        }
+    }
+
+    assert await async_setup_component(hass, "sensor", config)
+    await hass.async_block_till_done()
+
+    entity_ids = config["sensor"]["entities"]
+
+    for entity_id, value in dict(zip(entity_ids, VALUES)).items():
+        hass.states.async_set(entity_id, value)
+        await hass.async_block_till_done()
+        state = hass.states.get("sensor.test_last")
+        assert str(float(value)) == state.state
+        assert entity_id == state.attributes.get("last_entity_id")