TreeTableReportsNullAddedItems.java

import javafx.application.Application;
import javafx.beans.property.ReadOnlyStringProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.ListChangeListener;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.control.cell.TreeItemPropertyValueFactory;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

import java.util.List;

public class TreeTableReportsNullAddedItems extends Application {
    @Override
    public void start(final Stage primaryStage) throws Exception {
        // table items - 3 items, 2nd item has 2 children
        TreeItem<Item> root = new TreeItem<>();

        TreeItem<Item> two = new TreeItem<>(new Item("two"));
        two.getChildren().add(new TreeItem<>(new Item("childOne")));
        two.getChildren().add(new TreeItem<>(new Item("childTwo")));

        root.getChildren().add(new TreeItem<>(new Item("one")));
        root.getChildren().add(two);
        root.getChildren().add(new TreeItem<>(new Item("three")));

        // table columns - 1 column; name
        TreeTableColumn<Item, String> nameColumn = new TreeTableColumn<>("name");
        nameColumn.setCellValueFactory(new TreeItemPropertyValueFactory<>("name"));
        nameColumn.setPrefWidth(200);

        // table
        TreeTableView<Item> table = new TreeTableView<>();
        table.setShowRoot(false);
        table.setRoot(root);
        table.getColumns().addAll(nameColumn);
        table.getSelectionModel().getSelectedItems().addListener(this::processListChange);

        // version / info labels
        Label osLabel = new Label(System.getProperty("os.name"));
        Label jvmLabel = new Label(
                System.getProperty("java.version") +
                        "-" + System.getProperty("java.vm.version") +
                        " (" + System.getProperty("os.arch") + ")"
        );

        // scene /stage
        primaryStage.setScene(new Scene(
                new BorderPane(
                        table,
                        null,
                        null,
                        new VBox(osLabel, jvmLabel),
                        null
                )
        ));

        primaryStage.setWidth(600);
        primaryStage.setHeight(400);
        primaryStage.setTitle("SelectedTreeTableItems");
        primaryStage.show();
    }

    private void processListChange(ListChangeListener.Change<? extends TreeItem<Item>> c) {
        System.out.println("Change event...");
        while (c.next()) {
            System.out.println(" Change:");

            // ignore everything but added
            if (c.wasAdded()) {
                List<? extends TreeItem<Item>> addedList = c.getAddedSubList();
                addedList.forEach(item -> {
                    if(item == null) {
                        System.out.println("  WARNING: Added item was null.");
                    }
                    else {
                        System.out.println("  Added: " + item.getValue().getName());
                    }
                });
            }
        }
    }

    public static class Item {
        private final StringProperty name = new SimpleStringProperty("name");
        public final ReadOnlyStringProperty nameProperty() {return name;}
        public final String getName() {return name.get();}

        public Item(String name) {
            this.name.set(name);
        }
    }
}