How to load same fxml file again and again dynamically on the same window by clicking on the button?

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JavaFX

I am not able to add new tab functionality to browser.I already search a lot on google as well as on stackoverflow but nothing work.I want to load main fxml file again by clicking on new tab button.

Below is Main.java file

package tabcheck;
import javafx.application.Application;
//all imports..

public class Main extends Application{

public static void main(String[] args){
    launch(args);
}
@Override
public void start(Stage primaryStage) throws Exception {
   try{
       Parent root = FXMLLoader.load(getClass().getResource("/tabcheck/First page.fxml"));
       Scene scene = new Scene(root);
       scene.getStylesheets().add("tabcheck/application.css");
       primaryStage.setScene(scene);
       primaryStage.show();
      } 
      catch(Exception e){
       e.printStackTrace();}
   }
}

Below is controller of First-page.fxml

Home_controller.java
package tabcheck;
import java.io.IOException;
import java.net.URL;
//All imports...

public class Home_controller implements Initializable{
    @FXML private Button forward_btn;
    @FXML private Button refresh_btn;
    @FXML private Button go_btn;
    @FXML private TextField addressField;
    @FXML private WebView webView;
    @FXML private TabPane tabpane ;
    @FXML private BorderPane mainLayout;
    private Main main;
    private WebEngine webEngine;
      
     @Override
      public void initialize(URL url, ResourceBundle rb){
          webEngine = webView.getEngine();
          webEngine.load("http://www.google.com");
          webEngine.locationProperty().addListener(new ChangeListener<String>()        {
          @Override
          public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
              addressField.setText(newValue);
          }
         });
          addressField.setText("http://www.google.com");
        }

    public String fload(ActionEvent ae )
    {// code....
     }
     @FXML
     private void addTab() throws IOException{
         Tab tab = new Tab("New Tab");
         tabpane.getTabs().add(tab);
        // tabpane.getSelectionModel().clearSelection();
         FXMLLoader loader = new FXMLLoader();
         loader.setLocation(Main.class.getResource("/tabcheck/Tab-First-page.fxml"));
         AnchorPane tabAnchor = loader.load();
         tab.setContent(tabAnchor);
      }
}

In Controller class Tab-First-page.fxml is the copy of first-page.fxml and changes in Tab-first-page.fxml is that it does not contain Tabpane otherwise it is same.
I am able to load multiple tab from First-page.fxml but not able to open new tab from Tab-first-page.fxml that is, From main page multiple tabs can be open dynamically but from those open tabs I am not able to open new tabs. Following is the error I am getting...

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
**Caused by: java.lang.NullPointerException
at tabcheck.Home_controller.addTab(Home_controller.java:200)
... 62 more**
Home_controller.java:200 is tabpane.getTabs().add(tab); in addTab() method. I have tried every possible solution but not working,please any one can help?

What I have tried:

I have also try to do it by adding listener in addTab() but still null pointer exception is coming...also search on other websites but nothing is working...