A DESCRIPTION OF THE PROBLEM :
Run the attached code and you'll notice that treeTable.getSelectionModel().getSelectedItems() array contains 3 null elements when there is noting selected in the TreeTableView.


---------- BEGIN SOURCE ----------
package com.test;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeTableColumn;
import javafx.scene.control.TreeTableView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class TreeTable extends Application {
public static void main(String[] pArgs) {launch(pArgs);}

public void start(Stage pStage) {
final BorderPane pane = new BorderPane();
final Scene scene = new Scene(pane);
pStage.setScene(scene);

TreeTableView<String> treeTable = new TreeTableView<>();
TreeTableColumn<String,String> col = new TreeTableColumn<>("Column 1");
col.setCellValueFactory(features -> features.getValue().valueProperty());
treeTable.getColumns().add(col);
col = new TreeTableColumn<>("Column 2");
col.setCellValueFactory(features -> features.getValue().valueProperty());
treeTable.getColumns().add(col);

treeTable.setRoot(new TreeItem<>("root"));
treeTable.setShowRoot(false);
treeTable.getRoot().getChildren().add(new TreeItem<>("a"));
treeTable.getRoot().getChildren().add(new TreeItem<>("b"));
treeTable.getRoot().getChildren().add(new TreeItem<>("c"));

pane.setCenter(treeTable);
pStage.show();

treeTable.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
treeTable.getSelectionModel().selectAll();

treeTable.getRoot().getChildren().clear();

System.out.println("Elements: ");
for (TreeItem<String> item: treeTable.getSelectionModel().getSelectedItems()) {
if (item == null) {
System.out.println("null item");
} else {
System.out.println(item.getValue());
}
}
System.out.println();
}
}

---------- END SOURCE ----------