открытие javaFX окна много раз

Main.java

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application{
    public static void main(String[] args){
        launch();
    }
    @Override
    public void start(Stage primaryStage) throws Exception{
        FXMLLoader loader = new FXMLLoader(getClass().getResource("FirstWindow.fxml"));
        Parent root = loader.load();
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}

FirstWindowController.java

import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.stage.Stage;
import java.net.URL;
import java.util.ResourceBundle;
public class FirstWindowController implements Initializable{
    public Button btnOpenSecondWindow;
    public Label txtContent;
    @Override
    public void initialize(URL location, ResourceBundle resources){
        btnOpenSecondWindow.setOnAction(e -> {
            Parent root;
            try {
                FXMLLoader loader = new FXMLLoader(getClass().getResource("SecondWindow.fxml"));
                root = loader.load();
                Stage stage = new Stage();
                stage.setTitle("Second window");
                Scene scene = new Scene(root);
                stage.setScene(scene);
                stage.initOwner(btnOpenSecondWindow.getScene().getWindow());
                //SecondWindowController controller = loader.getController();
                //controller.someMethodCall();
                stage.showAndWait();
            } catch (Exception exc) {
                exc.printStackTrace();
            }
        });
    }
}

SecondWindowController.java

import javafx.fxml.Initializable;
import javafx.scene.control.Label;
import java.net.URL;
import java.util.ResourceBundle;
public class SecondWindowController implements Initializable{
    public Label txtContent;
    @Override
    public void initialize(URL location, ResourceBundle resources){
        //no-op
    }
}

FirstWindow.fxml

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.VBox?>
<VBox xmlns="http://javafx.com/javafx"
      xmlns:fx="http://javafx.com/fxml"
      fx:controller="FirstWindowController"
      prefHeight="200.0"
      prefWidth="200.0">
    <Label fx:id="txtContent"
           text="I am the first window!"/>
    <Button fx:id="btnOpenSecondWindow"
            text="Open second"/>
</VBox>

SecondWindow.fxml

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.Pane?>
<Pane xmlns="http://javafx.com/javafx"
      xmlns:fx="http://javafx.com/fxml"
      fx:controller="SecondWindowController"
      prefHeight="150.0"
      prefWidth="150.0">
    <Label fx:id="txtContent"
           text="I am the SECOND window!"/>
</Pane>

Структура проекта