Is there any way to load my .fxml after i call the class of my dialog controller?

I’m trying to call my dialog with a form inside it thats contain label to put name and button of sign in and cancel and it seems i got an exception when i load my fxml for the dialog.

additional question:

• On the AccountDialog, where a button get added to the dialogpane, any way hot to change the “OK” to “Sign In”?
• How to add an image for the background of my dialogpane?

// MainController where onLogin is handling the event
public class PlayerController {
    @FXML
    private Label userName;
    @FXML
    private BorderPane mainBorderPane;

    @FXML
    public void onLogin(ActionEvent e) {
        Dialog<Account> dialog = new AccountDialog(new Account(""));
        dialog.initOwner(mainBorderPane.getScene().getWindow());
        Optional<Account> result = dialog.showAndWait();
        result.ifPresent(account -> {
            userName.setText(account.getName());
        });
    }
}

// fxml file for PlayerController
<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>
<?import javafx.scene.layout.VBox?>

<BorderPane fx:id="mainBorderPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/21" xmlns:fx="http://javafx.com/fxml/1" fx:controller="hi.project.vidmot.audioplayer.PlayerController">
   <center>
      <GridPane prefWidth="500.0" BorderPane.alignment="CENTER">
        <columnConstraints>
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
          <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        </columnConstraints>
        <rowConstraints>
          <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
          <RowConstraints minHeight="0.0" prefHeight="0.0" valignment="BOTTOM" vgrow="NEVER" />
          <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
        </rowConstraints>
         <children>
            <Button maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" mnemonicParsing="false" text="Playlist 1" GridPane.columnIndex="0" GridPane.hgrow="ALWAYS" GridPane.vgrow="ALWAYS" />
            <Button maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" mnemonicParsing="false" text="Playlist2" GridPane.columnIndex="1" GridPane.hgrow="ALWAYS" GridPane.vgrow="ALWAYS" />
            <Button maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" mnemonicParsing="false" text="Playlist3" GridPane.hgrow="ALWAYS" GridPane.rowIndex="2" GridPane.vgrow="ALWAYS" />
            <Button maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" mnemonicParsing="false" text="Playlist4" GridPane.columnIndex="1" GridPane.hgrow="ALWAYS" GridPane.rowIndex="2" GridPane.vgrow="ALWAYS" />
         </children>
      </GridPane>
   </center>
   <left>
      <VBox BorderPane.alignment="CENTER">
         <children>
            <Button onAction="#onLogin" maxWidth="1.7976931348623157E308" mnemonicParsing="false" text="Sign in" />
            <Label fx:id="userName" alignment="CENTER" maxWidth="1.7976931348623157E308" prefHeight="35.0" prefWidth="100.0" text="Name" />
            <ScrollPane hbarPolicy="NEVER" prefWidth="100.0" vbarPolicy="ALWAYS" VBox.vgrow="ALWAYS" />
         </children>
      </VBox>
   </left>
</BorderPane>

// DialogController processing all things for the dialog
public class AccountDialog extends Dialog<Account> {
    private Account player;
    @FXML
    private TextField name;
    @FXML
    private GridPane gridPane;


    public AccountDialog(Account player) {
        super();
        this.setTitle("Sign in");
        readDialog();
        this.player = player;
    }

    private void readDialog(){
        FXMLLoader fxmlLoader = new FXMLLoader();
        fxmlLoader.setLocation(getClass().getResource("account-view.fxml"));
        try {
            this.getDialogPane().setContent(fxmlLoader.load());
        } catch (IOException e) {
            System.out.println("Couldn't load the dialog");
            e.printStackTrace();
        }

        this.getDialogPane().getButtonTypes().add(ButtonType.OK);
        this.getDialogPane().getButtonTypes().add(ButtonType.CANCEL);
    }

}

// fxml file for Dialog scene
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<DialogPane xmlns="http://javafx.com/javafx"
            xmlns:fx="http://javafx.com/fxml"
            fx:controller="hi.project.vidmot.audioplayer.AccountDialog">

    <content>
        <GridPane vgap="10" hgap="10">
            <Label text="Name: " GridPane.rowIndex="0" GridPane.columnIndex="0"/>
            <TextField fx:id="name" GridPane.rowIndex="0" GridPane.columnIndex="1"/>
        </GridPane>
    </content>

</DialogPane>

Let’s say i click a button and i want it showing the dialogpane with form on it and an image background.