Adjust REST schema validation (#81723)

fixes undefined

homeassistant/components/rest/schema.py

@@ -89,6 +89,13 @@ COMBINED_SCHEMA = vol.Schema(
 )
 
 CONFIG_SCHEMA = vol.Schema(
-    {DOMAIN: vol.All(cv.ensure_list, [COMBINED_SCHEMA])},
+    {
+        DOMAIN: vol.All(
+            # convert empty dict to empty list
+            lambda x: [] if x == {} else x,
+            cv.ensure_list,
+            [COMBINED_SCHEMA],
+        )
+    },
     extra=vol.ALLOW_EXTRA,
 )

tests/components/rest/test_init.py

@@ -18,7 +18,11 @@ from homeassistant.const import (
 from homeassistant.setup import async_setup_component
 from homeassistant.util.dt import utcnow
 
-from tests.common import async_fire_time_changed, get_fixture_path
+from tests.common import (
+    assert_setup_component,
+    async_fire_time_changed,
+    get_fixture_path,
+)
 
 
 @respx.mock
@@ -399,3 +403,17 @@ async def test_multiple_rest_endpoints(hass):
     assert hass.states.get("sensor.json_date_time").state == "07:11:08 PM"
     assert hass.states.get("sensor.json_time").state == "07:11:39 PM"
     assert hass.states.get("binary_sensor.binary_sensor").state == "on"
+
+
+async def test_empty_config(hass: HomeAssistant) -> None:
+    """Test setup with empty configuration.
+
+    For example (with rest.yaml an empty file):
+        rest: !include rest.yaml
+    """
+    assert await async_setup_component(
+        hass,
+        DOMAIN,
+        {DOMAIN: {}},
+    )
+    assert_setup_component(0, DOMAIN)