FeatureObject.java

/**
 * Staff feature title
 */
public class FeatureObject  {
    
    private String name;
    private String title;
    private boolean hidden;
    private ModuleObject module;
    
    public FeatureObject(){
        this.hidden= false;
        this.module= new ModuleObject();
    }
    
    /**
     * @param module ModuleObject owner
     * @param name String module unique name
     * @param title String module title
     */
    public FeatureObject(ModuleObject module, String name, String title){
        this.hidden= false;
        this.title= title;
        this.module = module;
        this.name= name;
    }
    
    /**
     * get feature name
     * @return String name
     */
    public String getName(){
        return this.name;
    }
    
    /**
     * get feature title
     * @return String title
     */
    public String getTitle(){
        return this.title;
    }
    
    /**
     * get module
     * @return ModuleObject module
     */
    public ModuleObject getModule() {
        return this.module;
    }
    
    /**
     * check if feature is hidden
     * @return boolean status
     */
    public boolean isHidden(){
        return this.hidden;
    }
    
    /**
     * set feature name
     * @param name String name
     */
    public void setName(String name){
        this.name= name;
    }
    
    /**
     * set feature title
     * @param title String title
     */
    public void setTitle(String title){
        this.title= title;
    }
    
    /**
     * hide feature 
     * @param hidden boolean status
     */
    public void setHidden(boolean hidden){
        this.hidden= hidden;
    }
    
    /**
     * set module
     * @param module ModuleObject
     */
    public void setModule(ModuleObject module) {
        this.module= module;
    }
}

form.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.*?>
<?import java.lang.*?>
<?import javafx.collections.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>

<VBox prefWidth="300.0" spacing="5.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1">
    <children>
        <Label styleClass="title-normal" text="Module:" />
        <AnchorPane>
            <children>
                <ComboBox fx:id="moduleField" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0" />
            </children>
        </AnchorPane>
        <Label styleClass="title-normal" text="Feature:" />
        <AnchorPane>
            <children>
                <ComboBox fx:id="featureField" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0" />
            </children>
        </AnchorPane>
    </children>
    <padding>
        <Insets bottom="5.0" left="5.0" right="5.0" />
    </padding>
</VBox>

ModuleFormLayout.java

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import javafx.beans.value.ObservableValue;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.collections.transformation.FilteredList;
import javafx.fxml.FXMLLoader;
import javafx.fxml.JavaFXBuilderFactory;
import javafx.scene.Node;
import javafx.scene.control.ComboBox;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.layout.VBox;
import javafx.util.Callback;
import javafx.util.StringConverter;

/**
 * module form layout
 */
public class ModuleFormLayout {
    
    private final VBox container;
    private ComboBox<ModuleObject> moduleField;
    private ComboBox<FeatureObject> featureField;
    
    private final ObservableList<ModuleObject> modules;
    private final ObservableList<FeatureObject> features;
    
    /**
     * @param modules List of modules
     * @param features List of features
     */
    public ModuleFormLayout(List<ModuleObject> modules, 
            List<FeatureObject> features){
        this.modules= FXCollections.observableArrayList(modules);
        this.features= FXCollections.observableArrayList(features);
        this.container= this.loadFormLayout();
    }
    
    /**
     * get layout container
     * @return VBox container
     */
    public VBox getContainer(){
        return this.container;
    }
    
    /**
     * fill form fields with values from current object
     */
    public void intFormValues(){
        this.moduleField.setItems(this.modules);
        this.featureField.setItems(this.features);
    }
    
    /**
     * initialize form and form fields
     * @return VBox form container
     */
    private VBox loadFormLayout() {
        VBox form= (VBox) ModuleFormLayout.readFxml("form.fxml");
        this.featureField= (ComboBox<FeatureObject>) form.lookup("#featureField");
        this.moduleField= (ComboBox<ModuleObject>) form.lookup("#moduleField");
        this.actionHandler();
        this.valueFactory();
        this.intFormValues();
        return form;
    }
    
    /**
     * read layout from FXML
     * this method is reused in other layouts
     * @param fxml String file name
     * @return Node read layout
     */
    public static Node readFxml(String fxml) {
        FXMLLoader loader = new FXMLLoader();
        InputStream in = ModuleFormLayout.class.getResourceAsStream(fxml);
        loader.setBuilderFactory(new JavaFXBuilderFactory());
        loader.setLocation(ModuleFormLayout.class.getResource(fxml));
        Node node = null;
        try {
            node = loader.load(in);
        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }
        return node;
    }
    
    /**
     * format variables to fit layout
     */
    private void valueFactory(){
        this.moduleValueFactory();
        this.featureValueFactory();
    }
    
    /**
     * format module variables to fit layout
     * this works fine
     */
    private void moduleValueFactory() {
        Callback<ListView<ModuleObject>, ListCell<ModuleObject>> module= 
            (ListView<ModuleObject> param) -> {
                ListCell<ModuleObject> cell = new ListCell<ModuleObject>() {
                    @Override
                    protected void updateItem(ModuleObject item, boolean empty) {
                        super.updateItem(item, empty);
                        if (item != null) {
                            this.setText(item.getTitle());
                        } else {
                            this.setText(null);
                        }
                    }
                };
                return cell;
            };
        this.moduleField.setConverter(new StringConverter<ModuleObject>() {
            @Override
            public String toString(ModuleObject object) {
                return object.getTitle();
            }
            @Override
            public ModuleObject fromString(String string) {
                return null;
            }
        });
        this.moduleField.setCellFactory(module);
        this.moduleField.setButtonCell(module.call(null));
    }
    
    /**
     * format feature variables to fit layout
     * this works fine
     */
    private void featureValueFactory() {
        Callback<ListView<FeatureObject>, ListCell<FeatureObject>> feature= 
            (ListView<FeatureObject> param) -> {
                ListCell<FeatureObject> cell = new ListCell<FeatureObject>() {
                    @Override
                    protected void updateItem(FeatureObject item, boolean empty) {
                        super.updateItem(item, empty);
                        if (item != null) {
                            this.setText(item.getTitle());
                        } else {
                            this.setText(null);
                        }
                    }
                };
                return cell;
            };
        this.featureField.setConverter(new StringConverter<FeatureObject>() {
            @Override
            public String toString(FeatureObject object) {
                return object.getTitle();
            }
            @Override
            public FeatureObject fromString(String string) {
                return null;
            }
        });
        this.featureField.setCellFactory(feature);
        this.featureField.setButtonCell(feature.call(null));
    }
    
    /**
     * handle actions
     * this is where error occurs
     */
    private void actionHandler(){
        //makesure module field is uptodate with selected feature
        //works fine
        this.featureField.valueProperty().addListener(
                (ObservableValue<? extends FeatureObject> observable, 
                        FeatureObject oldValue, FeatureObject newValue) -> {
            if (newValue!=null) {
                this.moduleField.setValue(newValue.getModule());
            }
        });
        
        //exception thrown here
        this.moduleField.valueProperty().addListener(
                (ObservableValue<? extends ModuleObject> observable, 
                        ModuleObject oldValue, ModuleObject newValue) -> {
            FilteredList<FeatureObject> feature = new FilteredList<>(this.features);
            feature.setPredicate((FeatureObject t) -> {
                if (newValue==null) {
                    return true;
                } else if (newValue.getName()==null || newValue.getName().equals("*")) {
                    return true;
                } else {
                    return t.getModule().getName().equals(newValue.getName());
                }
            });
            //setting this causes the exception
            this.featureField.setItems(feature);
        });
    }
}

ModuleObject.java

/**
 * Staff module title
 */
public class ModuleObject {
    
    private String name;
    private String title;
    private boolean hidden;
    
    public ModuleObject(){
        this.hidden= false;
    }
    
    /**
     * @param name String module unique name
     * @param title String module title
     */
    public ModuleObject(String name, String title){
        this();
        this.title= title;
        this.name= name;
    }
    
    /**
     * get module name
     * @return String name
     */
    public String getName(){
        return this.name;
    }
    
    /**
     * get module title
     * @return String title
     */
    public String getTitle(){
        return this.title;
    }
    
    /**
     * check if module is hidden
     * @return boolean status
     */
    public boolean isHidden(){
        return this.hidden;
    }
    
    /**
     * set module name
     * @param name String name
     */
    public void setName(String name){
        this.name= name;
    }
    
    /**
     * set module title
     * @param title String title
     */
    public void setTitle(String title){
        this.title= title;
    }
    
    /**
     * hide module 
     * @param hidden boolean status
     */
    public void setHidden(boolean hidden){
        this.hidden= hidden;
    }
}

Test.java

import java.util.Arrays;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.stage.Stage;

/**
 * testing layout
 */
public class Test extends Application {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }
    
    @Override
    public void start(Stage stage) throws Exception {
        stage.setTitle("Module Form");
        ModuleFormLayout form= this.testData();
        Scene scene= new Scene(form.getContainer());
        stage.setScene(scene);
        stage.show();
    }
    
    /**
     * add some testing data
     * @return ModuleFormLayout
     */
    private ModuleFormLayout testData(){
        ModuleObject all= new ModuleObject("*", "All");
        ModuleObject one= new ModuleObject("one", "Module One");
        ModuleObject two= new ModuleObject("two", "Module Two");
        FeatureObject all1= new FeatureObject(all, "all_1", "All Feature 1");
        FeatureObject one1= new FeatureObject(one, "one_1", "One Feature 1");
        FeatureObject one2= new FeatureObject(one, "one_2", "One Feature 2");
        FeatureObject one3= new FeatureObject(one, "one_3", "One Feature 3");
        FeatureObject two1= new FeatureObject(two, "two_1", "Two Feature 1");
        FeatureObject two2= new FeatureObject(two, "two_2", "Two Feature 2");
        FeatureObject two3= new FeatureObject(two, "two_3", "Two Feature 3");
        return new ModuleFormLayout(Arrays.asList(all, one, two), 
                Arrays.asList(all1, one1, one2, one3, two1, two2,two3));
    }
}