Java - Exception in Application start method - JavaFX

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

<?import java.lang.*?>

<?import java.util.*?>

<?import javafx.scene.*?>

<?import javafx.scene.control.*?>

<?import javafx.scene.layout.*?>

<AnchorPane id="AnchorPane" prefHeight="200" prefWidth="320" xmlns:fx="http://javafx.com/fxml/1" fx:controller="primerospasosjavafx.FXMLDocumentController">

    <children>

        <Button layoutX="126" layoutY="90" text="Click Me!" onAction="#handleButtonAction" fx:id="button" />

        <Label layoutX="126" layoutY="120" minHeight="16" minWidth="69" fx:id="label" />

    </children>

</AnchorPane>

/*

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package primerospasosjavafx;

import java.net.URL;

import java.util.ResourceBundle;

import javafx.event.ActionEvent;

import javafx.fxml.FXML;

import javafx.fxml.Initializable;

import javafx.scene.control.Label;

/*

 *

 * @author Documentos

 *

 */

public class FXMLDocumentController implements Initializable {

    @FXML

    private Label label;

    @FXML

    private void handleButtonAction(ActionEvent event) {

        System.out.println("You clicked me!");

        label.setText("Hello World!");

    }

    @Override

    public void initialize(URL url, ResourceBundle rb) {

        // TODO

    }

}

import javafx.application.Application;

import javafx.fxml.FXMLLoader;

import javafx.scene.Parent;

import javafx.scene.Scene;

import javafx.stage.Stage;

/**

 *

 * @author Documentos

 */

public class PrimerosPasosJavaFX extends Application {

    @Override

    public void start(Stage stage) throws Exception {

        Parent root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));

        Scene scene = new Scene(root);

        stage.setScene(scene);

        stage.show();

    }

    /**

     * @param args the command line arguments

     */

    public static void main(String[] args) {

        launch(args);

    }

}