javafx - problems doing setText on MenuButton - javafx

Question

So I have this code here:
// import statements are ommitted
public class HomePage implements Initializable{
#FXML
private volatile MenuButton fullUserName;
public void initialize(URL url, ResourceBundle resourceBundle)
{
}
public void loadHomePage(Stage primaryStage) throws IOException {
Parent HomePage = FXMLLoader.load(LoginScreen.class.getResource("HomePage.fxml"));
Timer animTimer = new Timer();
animTimer.scheduleAtFixedRate(new TimerTask() {
int i=0;
#Override
public void run() {
if (i<100) {
primaryStage.setX(primaryStage.getX() - 4);
primaryStage.setY(primaryStage.getY() - 1);
primaryStage.setWidth(primaryStage.getWidth()+8.11);
primaryStage.setHeight(primaryStage.getHeight()+3.19);
} else {
this.cancel();
}
i++;
}
}, 0, 10);
Timeline timeline = new Timeline(new KeyFrame(Duration.millis(10 * 101), ev -> {
primaryStage.setResizable(true);
primaryStage.setScene(new Scene(HomePage));
fullUserName.setText("User"); // Got NullPointerException at this line
}));
timeline.play();
}
public void start(Stage primaryStage) {
try {
Pane root = new Pane();
Scene scene = new Scene(root,400,400);
primaryStage.setScene(scene);
primaryStage.setResizable(false);
primaryStage.show();
loadHomePage(primaryStage);
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
HomePage.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.MenuButton?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.image.Image?>
<?import javafx.scene.image.ImageView?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>
<?import javafx.scene.text.Font?>
<?import javafx.scene.text.Text?>
<BorderPane maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" minHeight="9.0" minWidth="16.0" prefHeight="720.0" prefWidth="1280.0" xmlns="http://javafx.com/javafx/8.0.60" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.HomePage">
<top>
<GridPane maxHeight="-Infinity" minHeight="-Infinity" prefHeight="32.5" style="-fx-background-color: #aeccc9;" BorderPane.alignment="CENTER">
<columnConstraints>
<ColumnConstraints hgrow="SOMETIMES" maxWidth="-Infinity" minWidth="-Infinity" prefWidth="11.0" />
<ColumnConstraints hgrow="SOMETIMES" maxWidth="-Infinity" minWidth="-Infinity" prefWidth="27.5" />
<ColumnConstraints hgrow="SOMETIMES" maxWidth="-Infinity" minWidth="-Infinity" prefWidth="11.5" />
<ColumnConstraints hgrow="SOMETIMES" maxWidth="1.7976931348623157E308" minWidth="10.0" />
<ColumnConstraints hgrow="ALWAYS" maxWidth="-Infinity" minWidth="-Infinity" />
<ColumnConstraints hgrow="SOMETIMES" maxWidth="-Infinity" minWidth="-Infinity" prefWidth="15.0" />
</columnConstraints>
<rowConstraints>
<RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
</rowConstraints>
<children>
<MenuButton fx:id="fullUserName" mnemonicParsing="false" GridPane.columnIndex="4">
<items>
<MenuItem mnemonicParsing="false" text="Logout" />
<MenuItem mnemonicParsing="false" text="Exit" />
</items>
<graphic>
<ImageView fitHeight="22.0" fitWidth="22.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="#Cool-50.png" />
</image>
</ImageView>
</graphic>
<padding>
<Insets bottom="-1.5" left="-1.5" right="-1.5" top="-1.5" />
</padding>
</MenuButton>
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="Title" GridPane.columnIndex="3">
<font>
<Font name="Arial Rounded MT Bold" size="22.0" />
</font>
</Text>
</children>
</GridPane>
</top>
</BorderPane>
So as you can see, I got a NullPointerException when executing fullUserName.setText("User"); which means that the "fullUserName" menu button is not initialized.
Is it possible for the program to wait until fullUserName (or any other FXML variables for that matter) has been initialized so that I can execute the statement?