JavaFX TreeView setRoot出现异常

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) {
        TreeItem<String> rootItem = new TreeItem<>("Root");
        TreeView<String> treeView = new TreeView<>(rootItem);

        // 添加子节点
        TreeItem<String> childItem = new TreeItem<>("Child");
        rootItem.getChildren().add(childItem);

        // 设置根节点
        treeView.setRoot(rootItem);

        StackPane root = new StackPane(treeView);
        Scene scene = new Scene(root, 300, 200);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}