Install controlsFX in netbeans

I want to use the new controlsFX controls that I have downloaded from the controlsfx-8.40.10 file on the official website and installed it in SceneBuilder although some controls do not appear as thePopOver

I have also downloaded the repository and opened it in netbeans as a new project:

Next I have opened the sub project 'controlsfx' and I have copied the 'Source Packages' to my particular project:

My project is a miniprogram that just displays a controlFX called CustomTextField:

package pruebacontrolsfx;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import org.controlsfx.control.textfield.CustomTextField;

public class PruebaControlsFX extends Application {

    @Override
    public void start(Stage primaryStage) {
        CustomTextField customField = new CustomTextField();
        customField.setPromptText("Introduce texto");

        StackPane root = new StackPane();
        root.getChildren().add(customField); // genera un error ¿por qué?       
        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }  
}

But when I run it I get an error just when I add the control CustomTextFieldto a containerStackPane

What am I doing wrong?