bład przy dodawaniu Pane'a w javaFX

Witam
Piszę sobie programik okienkowy przy użyciu JavyFX i podczas dodawania zmiany widoku występuję błąd i nie mogę zlokalizować skąd on sie bierze. Może jakieś inne czujne oko coś wychwyci.

Klasa main:

package PFKmain;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class main extends Application {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		launch(args);
	}
	@Override
	public void start(Stage primaryStage) throws Exception {
		// TODO Auto-generated method stub
		FXMLLoader loader = new FXMLLoader(this.getClass().getResource("/FXML/main.fxml"));
		StackPane stackPane = loader.load();
		Scene scene=new Scene(stackPane,1280,800);
		primaryStage.setScene(scene);
		primaryStage.show();
	}
}

Klasa mainController:

package PFKcontrollers;

import java.io.IOException;

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;

public class MainController {

	@FXML
	private StackPane mainStackPane;

	public void initialize() {
		
		FXMLLoader loader = new FXMLLoader(getClass().getResource("/FXML/menuScreen.fxml"));
		Pane pane = null;
		try {
			pane = loader.load();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
MenuController menuController =loader.getController();
menuController.setMainController(this);
setScreen(pane);
	}

	public void setScreen(Pane pane) {
		mainStackPane.getChildren().add(pane);
	}
}

Klasa menuController:

package PFKcontrollers;

import java.io.IOException;

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.control.Button;
import javafx.scene.control.SplitPane;
import javafx.scene.layout.Pane;

public class MenuController {

	private MainController mainController;

	public void setMainController(MainController mainController) {
		this.mainController = mainController;
	}

	@FXML
	public void menuButton1() {
		FXMLLoader loader = new FXMLLoader(this.getClass().getResource("/FXML/option1.fxml"));
		Pane pane=null;
		try {
			pane=loader.load();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		mainController.setScreen(pane);
	}

	@FXML
	public void menuButton2() {

	}

	@FXML
	public void menuButton3() {

	}
}