Exception in thread "JavaFX Application Thread"

package combotest;
 
import javafx.application.Application;
import javafx.beans.InvalidationListener;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.ListCell;
import javafx.scene.control.SplitPane;
import javafx.scene.control.TextField;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
 
public class Main extends Application {
 
    private static final class ComBoxItemPerso {
 
        private final String value;
        private final Image icon;
 
        public ComBoxItemPerso(final String value, final String iconUrl) {
            this.value = value;
            this.icon = new Image(iconUrl);
        }
 
        public String getValue() {
            return value;
        }
 
        public Image getIcon() {
            return icon;
        }
    }
 
    private static final class ComBoxItemPersoListCell extends ListCell<ComBoxItemPerso> {
 
        private final ComboBox<ComBoxItemPerso> parent;
        private final Label rightLabel = new Label();
        private final ImageView leftImage = new ImageView();
        private final SplitPane splitPane = new SplitPane(leftImage, rightLabel);
 
        public ComBoxItemPersoListCell(final ComboBox<ComBoxItemPerso> parent) {
            super();
            // Oblige de rajouter tout ce qui suit a cause du splitpane.
            this.parent = parent;
            leftImage.setOnMousePressed(this::selectInCombo);
//            rightLabel.setStyle("-fx-border-color: green;");
            rightLabel.setMaxWidth(Double.MAX_VALUE);
            rightLabel.setOnMousePressed(this::selectInCombo);
        }
 
        private ComBoxItemPerso lastItem;
 
        @Override
        protected void updateItem(final ComBoxItemPerso item, final boolean empty) {
            super.updateItem(item, empty);
            lastItem = item;
            Node graphic = null;
            leftImage.setImage(null);
            rightLabel.setText(null);
            if (!empty && item != null) {
                leftImage.setImage(item.getIcon());
                rightLabel.setText(item.getValue());
                graphic = splitPane;
            }
            setGraphic(graphic);
            setText(null);
        }
 
        private void selectInCombo(final MouseEvent mouseEvent) {
            if (parent != null) {
                parent.getSelectionModel().select(lastItem);
            }
        }
    }
 
    private final TextField detailsTextField = new TextField();
    private final ComboBox<ComBoxItemPerso> myComboBox = new ComboBox<>();
 
    @Override
    public void start(Stage primaryStage) {
        detailsTextField.setEditable(false);
        //comboBox        
        myComboBox.setPrefWidth(176.5);
        final ObservableList<ComBoxItemPerso> options = FXCollections.observableArrayList(new ComBoxItemPerso("1", getClass().getResource("1.png").toExternalForm()),
                new ComBoxItemPerso("2", getClass().getResource("2.png").toExternalForm()),
                new ComBoxItemPerso("3", getClass().getResource("3.png").toExternalForm()));
        myComboBox.setItems(options);
        myComboBox.setButtonCell(new ComBoxItemPersoListCell(null));
        myComboBox.setCellFactory(listView -> new ComBoxItemPersoListCell(myComboBox));
        myComboBox.valueProperty().addListener(valueInvalidationListener);
        final StackPane center = new StackPane();
        center.getChildren().add(myComboBox);
        final BorderPane root = new BorderPane(center, detailsTextField, null, null, null);
        final Scene scene = new Scene(root, 300, 250);
        primaryStage.setTitle("Test");
        primaryStage.setScene(scene);
        primaryStage.show();
    }
 
    private final InvalidationListener valueInvalidationListener = observable -> {
        final ComBoxItemPerso item = myComboBox.getValue();
        final String text = (item == null) ? null : item.getValue();
        detailsTextField.setText(text);
    };
 
    public static void main(String[] args) {
        launch(args);
    }
 
}