Program: 78103
Project: 78103
Buggy source:
public void init(Stage stage) throws ServiceException {
  scrollPane.setHbarPolicy(ScrollPane.ScrollBarPolicy.NEVER);
  scrollPane.setVbarPolicy(ScrollPane.ScrollBarPolicy.AS_NEEDED);
  tile.setPadding(new Insets(20,20,20,20));
  tile.setHgap(20);
  tile.setVgap(20);
  List<at.ac.tuwien.sepm.ws16.qse01.entities.Image> listOfImages=imageService.getAllImages(1);
  for (  final at.ac.tuwien.sepm.ws16.qse01.entities.Image img : listOfImages) {
    HBox hBox=new HBox();
    hBox.setSpacing(120);
    hBox.setVisible(false);
    hBox.setStyle("String_Node_Str");
    ImageView fullscreen=new ImageView(getClass().getResource("String_Node_Str").toExternalForm());
    fullscreen.setFitHeight(30);
    fullscreen.setFitWidth(30);
    fullscreen.setOnMouseClicked(mouseEvent -> {
      LOGGER.debug("String_Node_Str");
      windowManager.showFullscreenImage();
    }
);
    ImageView delete=new ImageView(getClass().getResource("String_Node_Str").toExternalForm());
    delete.setFitHeight(30);
    delete.setFitWidth(30);
    delete.setOnMouseClicked((    MouseEvent mouseEvent) -> {
      LOGGER.debug("String_Node_Str");
      Alert alert=new Alert(Alert.AlertType.CONFIRMATION);
      alert.setHeaderText("String_Node_Str");
      alert.setContentText("String_Node_Str");
      alert.initModality(Modality.WINDOW_MODAL);
      alert.initOwner(stage);
      Optional<ButtonType> result=alert.showAndWait();
      if (result.isPresent() && result.get() == ButtonType.OK) {
        ImageView imageView=(ImageView)((VBox)(((ImageView)mouseEvent.getSource()).getParent().getParent())).getChildren().get(0);
        LOGGER.debug("String_Node_Str" + imageView.getId());
        try {
          imageService.delete(Integer.parseInt(imageView.getId()));
          tile.getChildren().remove(imageView.getParent());
          new File(String.valueOf(imageView.getUserData())).delete();
        }
 catch (        ServiceException e) {
          LOGGER.debug("String_Node_Str" + e.getMessage());
        }
      }
    }
);
    hBox.getChildren().addAll(fullscreen,delete);
    ImageView imageView=null;
    try {
      if (new File(img.getImagepath()).isFile()) {
        imageView=createImageView(new File(img.getImagepath()));
      }
 else       if (new File(System.getProperty("String_Node_Str") + "String_Node_Str" + img.getImagepath()).isFile()) {
        img.setImagepath(System.getProperty("String_Node_Str") + "String_Node_Str" + img.getImagepath());
        imageView=createImageView(new File(img.getImagepath()));
      }
 else {
        LOGGER.debug("String_Node_Str" + img.toString());
        imageService.delete(img.getImageID());
      }
      if (imageView != null) {
        VBox vBox=new VBox();
        LOGGER.debug("String_Node_Str" + img.getImageID());
        imageView.setId(String.valueOf(img.getImageID()));
        imageView.setUserData(img.getImagepath());
        vBox.getChildren().addAll(imageView,hBox);
        tile.getChildren().add(vBox);
      }
    }
 catch (    Exception e) {
      LOGGER.debug("String_Node_Str" + e.getMessage());
    }
  }
}

Fixed version (ground truth):
public void init(Stage stage) throws ServiceException {
  scrollPane.setHbarPolicy(ScrollPane.ScrollBarPolicy.NEVER);
  scrollPane.setVbarPolicy(ScrollPane.ScrollBarPolicy.AS_NEEDED);
  tile.setPadding(new Insets(20,20,20,20));
  tile.setHgap(20);
  tile.setVgap(20);
  List<at.ac.tuwien.sepm.ws16.qse01.entities.Image> listOfImages=imageService.getAllImages(1);
  for (  final at.ac.tuwien.sepm.ws16.qse01.entities.Image img : listOfImages) {
    HBox hBox=new HBox();
    hBox.setSpacing(120);
    hBox.setVisible(false);
    hBox.setStyle("String_Node_Str");
    ImageView fullscreen=new ImageView(new Image("String_Node_Str"));
    fullscreen.setFitHeight(30);
    fullscreen.setFitWidth(30);
    fullscreen.setOnMouseClicked(mouseEvent -> {
      LOGGER.debug("String_Node_Str");
      windowManager.showFullscreenImage();
    }
);
    ImageView delete=new ImageView(getClass().getResource("String_Node_Str").toExternalForm());
    delete.setFitHeight(30);
    delete.setFitWidth(30);
    delete.setOnMouseClicked((    MouseEvent mouseEvent) -> {
      LOGGER.debug("String_Node_Str");
      Alert alert=new Alert(Alert.AlertType.CONFIRMATION);
      alert.setHeaderText("String_Node_Str");
      alert.setContentText("String_Node_Str");
      alert.initModality(Modality.WINDOW_MODAL);
      alert.initOwner(stage);
      Optional<ButtonType> result=alert.showAndWait();
      if (result.isPresent() && result.get() == ButtonType.OK) {
        ImageView imageView=(ImageView)((VBox)(((ImageView)mouseEvent.getSource()).getParent().getParent())).getChildren().get(0);
        LOGGER.debug("String_Node_Str" + imageView.getId());
        try {
          imageService.delete(Integer.parseInt(imageView.getId()));
          tile.getChildren().remove(imageView.getParent());
          new File(String.valueOf(imageView.getUserData())).delete();
        }
 catch (        ServiceException e) {
          LOGGER.debug("String_Node_Str" + e.getMessage());
        }
      }
    }
);
    hBox.getChildren().addAll(fullscreen,delete);
    ImageView imageView=null;
    try {
      if (new File(img.getImagepath()).isFile()) {
        imageView=createImageView(new File(img.getImagepath()));
      }
 else       if (new File(System.getProperty("String_Node_Str") + "String_Node_Str" + img.getImagepath()).isFile()) {
        img.setImagepath(System.getProperty("String_Node_Str") + "String_Node_Str" + img.getImagepath());
        imageView=createImageView(new File(img.getImagepath()));
      }
 else {
        LOGGER.debug("String_Node_Str" + img.toString());
        imageService.delete(img.getImageID());
      }
      if (imageView != null) {
        VBox vBox=new VBox();
        LOGGER.debug("String_Node_Str" + img.getImageID());
        imageView.setId(String.valueOf(img.getImageID()));
        imageView.setUserData(img.getImagepath());
        vBox.getChildren().addAll(imageView,hBox);
        tile.getChildren().add(vBox);
      }
    }
 catch (    Exception e) {
      LOGGER.debug("String_Node_Str" + e.getMessage());
    }
  }
}