Fix KNX expose default value when attribute is `None` (#103446)

Fix KNX expose default value when attribute is `null`

homeassistant/components/knx/expose.py

@@ -122,12 +122,12 @@ class KNXExposeSensor:
         """Extract value from state."""
         if state is None or state.state in (STATE_UNKNOWN, STATE_UNAVAILABLE):
             value = self.expose_default
+        elif self.expose_attribute is not None:
+            _attr = state.attributes.get(self.expose_attribute)
+            value = _attr if _attr is not None else self.expose_default
         else:
-            value = (
-                state.state
-                if self.expose_attribute is None
-                else state.attributes.get(self.expose_attribute, self.expose_default)
-            )
+            value = state.state
+
         if self.expose_type == "binary":
             if value in (1, STATE_ON, "True"):
                 return True

tests/components/knx/test_expose.py

@@ -85,6 +85,14 @@ async def test_expose_attribute(hass: HomeAssistant, knx: KNXTestKit) -> None:
     hass.states.async_set(entity_id, "off", {})
     await knx.assert_telegram_count(0)
 
+    # Change attribute; keep state
+    hass.states.async_set(entity_id, "on", {attribute: 1})
+    await knx.assert_write("1/1/8", (1,))
+
+    # Change state to "off"; null attribute
+    hass.states.async_set(entity_id, "off", {attribute: None})
+    await knx.assert_telegram_count(0)
+
 
 async def test_expose_attribute_with_default(
     hass: HomeAssistant, knx: KNXTestKit
@@ -132,6 +140,14 @@ async def test_expose_attribute_with_default(
     hass.states.async_set(entity_id, "off", {})
     await knx.assert_write("1/1/8", (0,))
 
+    # Change state and attribute
+    hass.states.async_set(entity_id, "on", {attribute: 1})
+    await knx.assert_write("1/1/8", (1,))
+
+    # Change state to "off"; null attribute
+    hass.states.async_set(entity_id, "off", {attribute: None})
+    await knx.assert_write("1/1/8", (0,))
+
 
 async def test_expose_string(hass: HomeAssistant, knx: KNXTestKit) -> None:
     """Test an expose to send string values of up to 14 bytes only."""