Allow trigger based numeric sensors to be set to unknown (#137047)

* Allow trigger based numeric sensors to be set to unknown

* resolve comments

* Do case insensitive check

* use _parse_result

---------

Co-authored-by: abmantis <amfcalt@gmail.com>

homeassistant/components/template/sensor.py

@@ -339,6 +339,7 @@ class TriggerSensorEntity(TriggerEntity, RestoreSensor):
         """Initialize."""
         super().__init__(hass, coordinator, config)
 
+        self._parse_result.add(CONF_STATE)
         if (last_reset_template := config.get(ATTR_LAST_RESET)) is not None:
             if last_reset_template.is_static:
                 self._static_rendered[ATTR_LAST_RESET] = last_reset_template.template

tests/components/template/test_sensor.py

@@ -1527,6 +1527,45 @@ async def test_trigger_entity_available(hass: HomeAssistant) -> None:
     assert state.state == "unavailable"
 
 
+@pytest.mark.parametrize(("source_event_value"), [None, "None"])
+async def test_numeric_trigger_entity_set_unknown(
+    hass: HomeAssistant, source_event_value: str | None
+) -> None:
+    """Test trigger entity state parsing with numeric sensors."""
+    assert await async_setup_component(
+        hass,
+        "template",
+        {
+            "template": [
+                {
+                    "trigger": {"platform": "event", "event_type": "test_event"},
+                    "sensor": [
+                        {
+                            "name": "Source",
+                            "state": "{{ trigger.event.data.value }}",
+                        },
+                    ],
+                },
+            ],
+        },
+    )
+    await hass.async_block_till_done()
+
+    hass.bus.async_fire("test_event", {"value": 1})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.source")
+    assert state is not None
+    assert state.state == "1"
+
+    hass.bus.async_fire("test_event", {"value": source_event_value})
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.source")
+    assert state is not None
+    assert state.state == STATE_UNKNOWN
+
+
 async def test_trigger_entity_available_skips_state(
     hass: HomeAssistant, caplog: pytest.LogCaptureFixture
 ) -> None: