问FXMLLoader getController()返回null

EN

@FXML
private void handleBtnAdicionarAction(ActionEvent event) throws IOException {   
    Stage adicionarStage = new Stage();
    FXMLLoader loader = new FXMLLoader(getClass().getResource("/fxml/AdicionarWindow.fxml"));
    Parent root = (Parent) loader.load();
    Scene scene = new Scene(root);
    adicionarStage.setScene(scene);
    adicionarStage.centerOnScreen();
    adicionarStage.show();
    awUI = loader.getController();
    System.out.println(awUI);
    awUI.associarController(this);
}