fixup! Implement ExposedThing functionality

Author: JKRhb

lib/src/core/implementation/exposed_thing.dart

@@ -289,11 +289,13 @@ class ExposedThing implements scripting_api.ExposedThing, ExposableThing {
 
   @override
   Stream<Content> handleObserveProperty(
-    String eventName, {
+    String propertyName, {
     int? formIndex,
     Map<String, Object>? uriVariables,
     Object? data,
   }) {
+    final property = _obtainProperty(propertyName);
+
     // TODO: implement handleObserveProperty
     throw UnimplementedError();
   }