Fix MQTT JSON light restoring None color_mode on startup

homeassistant/components/mqtt/light/schema_json.py

@@ -337,8 +337,8 @@ async def _subscribe_topics(self) -> None:
             self._attr_brightness = last_attributes.get(
                 ATTR_BRIGHTNESS, self.brightness
             )
-            self._attr_color_mode = last_attributes.get(
-                ATTR_COLOR_MODE, self.color_mode
+            self._attr_color_mode = (
+                last_attributes.get(ATTR_COLOR_MODE) or self.color_mode
             )
             self._attr_color_temp_kelvin = last_attributes.get(
                 ATTR_COLOR_TEMP_KELVIN, self.color_temp_kelvin

tests/components/mqtt/test_light_json.py

@@ -565,6 +565,63 @@ async def test_single_color_mode_turn_on(
     assert state.state == STATE_ON
 
 
+@pytest.mark.parametrize(
+    "hass_config",
+    [
+        {
+            mqtt.DOMAIN: {
+                light.DOMAIN: {
+                    "schema": "json",
+                    "name": "test",
+                    "command_topic": "test_light/set",
+                    "supported_color_modes": ["brightness"],
+                }
+            }
+        },
+        {
+            mqtt.DOMAIN: {
+                light.DOMAIN: {
+                    "schema": "json",
+                    "name": "test",
+                    "command_topic": "test_light/set",
+                    "supported_color_modes": ["color_temp"],
+                }
+            }
+        },
+    ],
+)
+async def test_restore_state_with_none_color_mode(
+    hass: HomeAssistant, mqtt_mock_entry: MqttMockHAClientGenerator
+) -> None:
+    """Test restoring state with a None color_mode does not break turn_on.
+
+    Regression test: When an optimistic light was off at the time the state
+    was last saved, `state_attributes` stores `color_mode: None`. On restart,
+    the restore path would overwrite the correctly initialized color_mode with
+    None, causing turn_on to raise "does not report a color mode".
+    """
+    fake_state = State(
+        "light.test",
+        STATE_OFF,
+        {"color_mode": None, "brightness": None},
+    )
+    mock_restore_cache(hass, (fake_state,))
+
+    mqtt_mock = await mqtt_mock_entry()
+
+    state = hass.states.get("light.test")
+    assert state.state == STATE_OFF
+
+    # This should not raise "does not report a color mode"
+    await common.async_turn_on(hass, "light.test")
+    mqtt_mock.async_publish.assert_called_once_with(
+        "test_light/set", '{"state":"ON"}', 0, False
+    )
+    state = hass.states.get("light.test")
+    assert state.state == STATE_ON
+    assert state.attributes.get("color_mode") is not None
+
+
 @pytest.mark.parametrize(
     "hass_config",
     [