title: NullPointerException while modyfing elements on second Pane JavaFX
body: <p>I have a problem with nullPointer while i'm trying to modify any element from second Panel in my application.
  How my application look like: I have 2 Panel, first to loggin and second one with Main Application.
  Steps in my application:</p>
  
  <ol>
  <li>Create and show 1 panel</li>
  <li>Provide passwords and loggin to database
  a/ Success - open new panel and hide this one
  b/ show error message</li>
  <li>Now i'm trying to modify any element from panel 2 but i cant</li>
  </ol>
  
  
  
  <pre><code>Caused by: java.lang.NullPointerException
      at sample.ControllerLoginMenu.openScene(ControllerLoginMenu.java:114)
      at sample.ControllerLoginMenu.login(ControllerLoginMenu.java:41)
      ... 58 more
  </code></pre>
  
  <p>Here is my code </p>
  
  <pre><code>public class ControllerLoginMenu {
  @FXML private Label statusMessage; // second Panel
  @FXML private Circle statusCircle; // second Panel
  @FXML private Label errorMessageConnection; // First Panel
  @FXML private Label errorMessagePassword;   // First Panel
  @FXML private TextField loginField;         //First Panel
  @FXML private PasswordField passwordField;  //First panel
  private String username ;
  private String password ;
  private final String url = "jdbc:oracle:thin:@google.com:6666:NotExist";
  private Stage primaryStage = new Stage();
  private Connection con;
  private Statement statement;
  @FXML private void login(ActionEvent event) throws IOException {
      checkConnection();
      openScene(event);
      // From there is the problem'
      errorMessageConnection.setVisible(true); -- no Error
      statusCircle.setFill(Color.RED); -- Error
  }
  private void openScene(ActionEvent event) throws IOException {
      Parent root = FXMLLoader.load(getClass().getResource("MainMenu.fxml"));
      ((Node) event.getSource()).getScene().getWindow().hide();
      primaryStage.setTitle("Masterdata loading application");
      primaryStage.setScene(new Scene(root, 640, 480));
      primaryStage.show();
  }
  private boolean checkConnection()   {
  
      boolean result = false;
      try {
          Class.forName("oracle.jdbc.driver.OracleDriver");
  
      } catch (ClassNotFoundException e) {
          e.printStackTrace();
          return result;
      }
      try {
          con = DriverManager.getConnection(url, username, password);
          statement = con.createStatement();
          String sql = "SELECT SYSDATE FROM DUAL";
          result  = statement.execute(sql);
      }
      catch (SQLException e)
      {
          passwordField.setText("");
          e.printStackTrace();
          return result;
      }
      return result;
  }
  private boolean getPasswords()
  {
      username = loginField.getText();
      password = passwordField.getText();
      if(username.isEmpty() || password.isEmpty())
          return false;
      else
          return true;
  }
  @Override // Main Class
  public void start(Stage primaryStage) throws Exception{
      Parent root = FXMLLoader.load(getClass().getResource("LoginMenu.fxml"));
      primaryStage.setTitle("Masterdata loading application");
      primaryStage.setScene(new Scene(root, 540, 380));
      primaryStage.show();
  }
  </code></pre>
  
  <p>I other posts i have found that this should solve problem, but it didnt.</p>
  
  <pre><code>Platform.runLater(() -&gt;{
  statusCircle.setFill(Color.GREEN);});
  </code></pre>