Fix mqtt is not reloading without yaml config (#103159)

homeassistant/components/mqtt/__init__.py

@@ -233,7 +233,7 @@ async def async_check_config_schema(
 ) -> None:
     """Validate manually configured MQTT items."""
     mqtt_data = get_mqtt_data(hass)
-    mqtt_config: list[dict[str, list[ConfigType]]] = config_yaml[DOMAIN]
+    mqtt_config: list[dict[str, list[ConfigType]]] = config_yaml.get(DOMAIN, {})
     for mqtt_config_item in mqtt_config:
         for domain, config_items in mqtt_config_item.items():
             schema = mqtt_data.reload_schema[domain]

tests/components/mqtt/test_init.py

@@ -3974,3 +3974,39 @@ async def test_reload_with_invalid_config(
 
     # Test nothing changed as loading the config failed
     assert hass.states.get("sensor.test") is not None
+
+
+@pytest.mark.parametrize(
+    "hass_config",
+    [
+        {
+            "mqtt": [
+                {
+                    "sensor": {
+                        "name": "test",
+                        "state_topic": "test-topic",
+                    }
+                },
+            ]
+        }
+    ],
+)
+async def test_reload_with_empty_config(
+    hass: HomeAssistant,
+    mqtt_mock_entry: MqttMockHAClientGenerator,
+) -> None:
+    """Test reloading yaml config fails."""
+    await mqtt_mock_entry()
+    assert hass.states.get("sensor.test") is not None
+
+    # Reload with an empty config and assert again
+    with patch("homeassistant.config.load_yaml_config_file", return_value={}):
+        await hass.services.async_call(
+            "mqtt",
+            SERVICE_RELOAD,
+            {},
+            blocking=True,
+        )
+        await hass.async_block_till_done()
+
+    assert hass.states.get("sensor.test") is None