Unable to load new scene from JavaFX FXML menubar

Question

I'm developing a JavaFX application using FXML and scene builder but I'm stuck with loading a new window using a menu bar option.

I click the menu bar option and using the code, I pass parameters to a window changer method however the error I get back is a java.lang.NullPointerException indicating the parameters I'm attempting to pass to the method are in fact not, leading the values to be null.

The exact error is: Caused by: java.lang.NullPointerException: Cannot invoke "javafx.stage.Stage.setTitle(String)" because "this.stage" is null

I have a window changer controller with this method:

public class WindowChanger

private Stage stage;
private Scene scene;
private Parent parent;

public void changeToNewRecordWindow(ActionEvent newRecordClick, String windowView, String windowTitle) throws IOException {
    FXMLLoader loader = new FXMLLoader();
    loader.setLocation(getClass().getResource(windowView));
    parent = loader.load();
    scene = new Scene(parent);

    stage.setTitle(windowTitle);

    stage = (Stage) parent.getScene().getWindow();

    stage.setScene(scene);
    stage.show();
}

The main application controller file has this method:

public class MainApplicationController  {

WindowChanger sc;

    @FXML
protected void newRecord(ActionEvent newRecordClick) throws IOException {
    sc = new WindowChanger();
    sc.changeToNewRecordWindow(newRecordClick, "/application/NewHealthRecordView.fxml", "Create New Record");
}
}

with this MainAppView.fxml:

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

<?import javafx.scene.control.Label?>
<?import javafx.scene.control.Menu?>
<?import javafx.scene.control.MenuBar?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Font?>

<VBox prefHeight="400.0" prefWidth="640.0" xmlns="http://javafx.com/javafx/19" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.MainApplicationController">
    <children>
        <AnchorPane maxHeight="-1.0" maxWidth="-1.0" prefHeight="-1.0" prefWidth="-1.0" VBox.vgrow="ALWAYS">
            <children>
              <MenuBar prefHeight="27.0" prefWidth="640.0">
                  <menus>
                      <Menu mnemonicParsing="false" text="Records">
                          <items>
                              <MenuItem mnemonicParsing="false" onAction="#newRecord" text="New" />
                          </items>
                      </Menu>                     
                      <Menu mnemonicParsing="false" text="Exit Program">
                          <items>
                              <MenuItem mnemonicParsing="false" onAction="#closeClicked" text="Exit Program" />
                          </items>
                  </Menu>
                  </menus>
              </MenuBar>
                <Label alignment="CENTER" layoutX="155.0" layoutY="177.0" style="&#10;" text="Main window data to be done" textAlignment="CENTER" textFill="#9f9f9f" wrapText="false">
                    <font>
                        <Font size="18.0" />
                    </font>
                </Label>
            </children>
        </AnchorPane>
    </children>
</VBox>

Which I'm then trying to call this FXML

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

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ComboBox?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.AnchorPane?>

<AnchorPane prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/19" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.NewHealthRecordController">
   <children>
      <Label layoutX="62.0" layoutY="28.0" prefHeight="19.0" prefWidth="45.0" text="Label 0" />
      <Label layoutX="62.0" layoutY="72.0" text="Label 1" />
      <Label layoutX="62.0" layoutY="113.0" text="Label 2" />
      <Label layoutX="62.0" layoutY="158.0" text="Label 3" />
      <Label layoutX="178.0" layoutY="158.0" text="Label 4" />
      <Label layoutX="339.0" layoutY="158.0" text="Leabel 5" />
      <Label layoutX="62.0" layoutY="194.0" text="Label 6" />
      <ComboBox editable="true" layoutX="178.0" layoutY="25.0" prefWidth="150.0" promptText="Choose date..." />
      <TextField layoutX="179.0" layoutY="68.0" />
      <TextField layoutX="179.0" layoutY="109.0" />
      <TextField layoutX="214.0" layoutY="154.0" prefHeight="25.0" prefWidth="79.0" />
      <TextField layoutX="376.0" layoutY="154.0" prefHeight="25.0" prefWidth="79.0" />
      <TextArea layoutX="102.0" layoutY="194.0" prefHeight="124.0" prefWidth="358.0" />
      <Button layoutX="141.0" layoutY="343.0" mnemonicParsing="false" text="Submit" />
      <Button layoutX="325.0" layoutY="343.0" mnemonicParsing="false" text="Cancel" />
   </children>
</AnchorPane>

It seems similar to this question question however i'm not sure where the 'fx:id' for the AnchorPane should go and then how to call it from the WindowChanger class.

Can anyone provide guidance on where I might be missing passing the values correctly?

EDIT: @James_D below pointed it out but I found that if i used this code:

        FXMLLoader loader = new FXMLLoader(getClass().getResource(windowView));
        parent = loader.load();
        stage = new Stage();

        stage.setTitle(windowTitle);
        stage.setScene(new Scene(parent));
        stage.show();

it worked but I didn't quite know why. Now I see I added

stage = new Stage();