Calling methods in a Java Fx ActionEvent

I'm new to JavaFX and I want to create a view class that will call methods in a Controller when an event is triggered by a button push. My code is below:

package spacetrader.menu;

import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.layout.Pane;
import spacetrader.Window;

public class MenuView implements Initializable {
    public Window window;
    public MenuCtrl menuCtrl;

    @FXML
    Button start;
    @FXML
    Pane background;
    @FXML
    Button exit;

    public MenuView() {};

    public MenuView(Window aWindow, MenuCtrl aMenuCtrl) {
        window = aWindow;
        menuCtrl = aMenuCtrl;
    }

    void renderMainMenu() {
        try {
            window.loadFXML(new FXMLLoader((getClass().getResource("MainMenu.fxml"))));
        } catch (IOException ex) {
            Logger.getLogger(MenuView.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        start.setOnAction((ActionEvent event) -> menuCtrl.newGame());
        exit.setOnAction((ActionEvent event) -> menuCtrl.closeApplication());
    }
}

This compiles, but when I run it and press the button I get a null pointer exception on the lambda expressions. The exception refers to "menuCtrl." How should I be setting up my program to make the button call menuCtrl.newGame()?

Here's what I've tried already:

• I've moved the setOnAction commands to between the various methods.
• Replaced the calls to menuCtrl methods with System.out.prinln statements to confirm that this works. It does.
• I've replaced menuCtrl methods with System.out.println(this) to ensure there isn't a scoping problem. It prints "spacetrader.menu.MenuView@74f51979" as expected.
• Converted the Lambda expressions to anonymous inner classes
• Used a block as the lambda's body