Refactor: Cleanup code

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

@@ -81,6 +81,7 @@ import javafx.scene.control.TreeView;
 import javafx.scene.paint.Color;
 import javafx.stage.FileChooser;
 import javafx.stage.FileChooser.ExtensionFilter;
+import org.jspecify.annotations.NonNull;
 
 public class CityDoctorController {
 
@@ -1604,12 +1605,11 @@ public class CityDoctorController {
         return model;
     }
 
-    public CityObject retrieveCityObject(GmlId gmlId) {
+    public @NonNull CityObject retrieveCityObject(GmlId gmlId) {
         try{
             return model.getCityObject(gmlId);
         }catch(IllegalArgumentException e){
-            logger.warn(e.getMessage());
-            return null;
+            throw new NullPointerException(e.getMessage());
         }
     }
 

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

@@ -37,6 +37,7 @@ import javafx.scene.transform.Rotate;
 import javafx.stage.Stage;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.jspecify.annotations.NonNull;
 
 import javax.imageio.ImageIO;
 import java.awt.image.BufferedImage;
@@ -831,7 +832,7 @@ public class MainWindow extends Application {
         node.getFeatureExportAction(this);
     }
 
-    public CityObject retrieveCityObject(GmlId id){
+    public @NonNull CityObject retrieveCityObject(GmlId id){
         return controller.retrieveCityObject(id);
     }