add entry to my database in JavaFx

Question

I'm trying to made a graphical window to add entry to a database in javafx. No problem to display the 'add entry' window, however impossible to add the entry and then refresh my database. I get a NullPointerException on getPers and CreatePerson

I tried a lot of things to initialize these variables without success. How can I do that?

Here is my class 'addPers'

public class addPers {

    @FXML
    private TextField nameField;

    @FXML
    private TextField ageField;

    @FXML
    private Button Cancel;

    @FXML
    private Button CreatePerson;


    private Stage dialogStage;
    private Pers pers;

    private boolean okClicked = false;
    private MainApp mainApp;
    private PersManager persManager;
    private AnchorPane databaseLayout;
    private Object databaseLayoutController;
    private Object rootLayout;

    @FXML
    private void initialize() {
    }


    public void setDialogStage(Stage dialogStage) {
        this.dialogStage = dialogStage;
    }

    public void setPers(Pers pers) {
        this.pers = pers;

        nameField.setText(pers.getName());
        ageField.setText(Integer.toString(pers.getAge()));

    }


    @FXML
    private void Cancel() {
        dialogStage.close();
    }

    @FXML
    public void CreatePerson(ActionEvent event) throws Exception{

        // Check Form Validation;
        Alert alert = new Alert(AlertType.ERROR);
        alert.setTitle("Please input carefully");
        alert.setHeaderText(null);

        if(nameField.getText().equals("")){
            alert.setContentText("no valid name");
            alert.showAndWait();
        }
        else if(ageField.getText().equals("")){
            alert.setContentText("no valid age");
            alert.showAndWait();
        }

        else{

            getPers();
            // Display Dialogue;
            alert.setAlertType(AlertType.INFORMATION);;
            alert.setContentText("Person entry created successfully");
            alert.showAndWait();
        }

            // Change scene;
            Stage stage = (Stage) CreatePerson.getScene().getWindow();
            Scene scene = CreatePerson.getScene();
            FXMLLoader loader = new FXMLLoader(getClass().getResource("../views/Database.fxml"));
            scene.setRoot(loader.load());
            stage.setScene(scene);
            stage.setTitle("alt database");
            stage.show();

        }

        public ArrayList<Pers> getPers() throws SQLException {
            ArrayList<Pers> ListPers = new ArrayList<Pers>();
            String query = "name, age FROM PERSONS_DB ORDER BY name;";

            try {
                ((MainApp) this.mainApp).getDatabase().connect();
                ResultSet rslt = ((MainApp) this.mainApp).getDatabase().getResultOf(query);
                while (rslt.next()) {
                    ListPers.add(new Pers
                           (rslt.getString("name"),
                            rslt.getInt("age")
                            ));
                }
                rslt.close();



             try {
                    mainApp.showDatabaseDialog();

                 FXMLLoader loader = new FXMLLoader();

                 AnchorPane databaseEditDialog = (AnchorPane) loader.load();
                 DatabaseEditController controller = loader.getController();
                 Stage dialogStage = new Stage();
                 dialogStage.setTitle("database");
                 dialogStage.initModality(Modality.WINDOW_MODAL);
                 Window primaryStage = null;
                dialogStage.initOwner(primaryStage);
                 Parent page = null;
                Scene scene = new Scene(page);
                 dialogStage.setScene(scene);
                 dialogStage.show();

             } catch (IOException e) {
                 e.printStackTrace();
             }
        } finally {
        }
    return ListPers;
         }

        public void setMainApp(MainApp mainApp) {
            this.mainApp = mainApp;

        }

}