Refactor fetching of top-level CityObject

CityDoctorParent/Extensions/CityDoctorGUI/src/main/java/de/hft/stuttgart/citydoctor2/gui/VertexClickHandler.java

@@ -49,25 +49,19 @@ public class VertexClickHandler implements ClickHandler {
 
 			MenuItem clipMi = new MenuItem(Localization.getText("MainWindow.copyId"));
 			clipMi.setOnAction(ea -> {
-				CityObject parent = p.getParent().getParent();
-				if (parent instanceof BoundarySurface bs) {
-					parent = bs.getParent();
-
-				}
+				CityObject topLevelCityObject = p.getParent().getParent().getTopLevelCityObject();
 				Clipboard clipboard = getSystemClipboard();
 				ClipboardContent content = new ClipboardContent();
-				content.putString(parent.getGmlId().toString());
+				content.putString(topLevelCityObject.getGmlId().toString());
 				clipboard.setContent(content);
 			});
 			cMenu.getItems().add(clipMi);
 
 			MenuItem detailMi = new MenuItem(Localization.getText("MainWindow.focusCityObject"));
 			detailMi.setOnAction(ea -> {
-				CityObject parent = p.getParent().getParent();
-				if (parent instanceof BoundarySurface bs) {
-					parent = bs.getParent();
-				}
-				mainWindow.showCityObjectDetail(parent);
+				CityObject topLevelCityObject = p.getParent().getParent().getTopLevelCityObject();
+				mainWindow.showCityObjectDetail(topLevelCityObject);
+
 			});
 			cMenu.getItems().add(detailMi);