Blank JavaFX window

Question

This is the JavaFX program which suppose to show player cards but it shows a blank window. I tried to clean and build but nothing has happened. Also, there no error showing as well. I checked The image path and it's totally correct. In that case, I wonder why it didn't show the cards in the window. There is no other classes other than this one.

Images are named as 1.png, 2.png, 3.png... until 54.png

https://www.dropbox.com/sh/bzl2jya6plldvc0/AADMbPhYalS7sgpeDZdoRKlWa?dl=0

import java.util.ArrayList;
import java.util.Random;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

/**
 *
 * @author Ramitha
 */
public class JavaFXAssignment extends Application{

//Creating class JavaFXCardGUI which is extending Application class
//Now JavaFXCardGUI class will act as an JavaFX Application
 //Overriding start method of Application class which is always a starting point of any JavaFX Application
   @Override
   public void start(Stage primaryStage) throws Exception {

       //Creating a VBox object
       VBox vBox=new VBox();
       //Setting its spacing and padding
       vBox.setSpacing(50);
       vBox.setPadding(new Insets(20, 40, 40, 60));

       //Creating a HBox object which will store the first row cards and setting its spacing property
       HBox firstRowHBox=new HBox();
       firstRowHBox.setSpacing(50);

       //Creating a HBox object which will store the second row cards and setting its spacing property
       HBox secondRowHBox=new HBox();
       secondRowHBox.setSpacing(50);

       //Creating a HBox object which will store the third row cards and setting its spacing property
       HBox thirdRowHBox=new HBox();
       thirdRowHBox.setSpacing(50);

       //Creating a arraylist of unique 52 cards which will store the each card number
       //If that card number will be already present in the arraylist then that card will not be added
       ArrayList<Integer> lstUnique52Cards=new ArrayList<Integer>();

       //Creating a random class object
       Random random=new Random();

      //This loop will add the three cards in first row
       while(lstUnique52Cards.size()<3) {
           //Generate a randomNumber between 1 and 52 both inclusive
           //Since random.NextInt(52) will return number from 0 to 51 Hence adding 1 to
           //make it from 1 to 52
           int randomNumber=random.nextInt(52)+1;

           //If the current random generated is not present in the array list lstUnique52Cards
           //it means that the random number is unique then add that random number in array list lstUnique52Cards
           //then create the correpsonding ImageView with the card number represented by randomNumber
           //Then add the image to the firstRowHBox
           if(!lstUnique52Cards.contains(randomNumber)) {
               lstUnique52Cards.add(randomNumber);
               ImageView imgViewCard=new ImageView(new Image("file:C:\\Users\\JavaFXCards\\card"+randomNumber+".png"));
               firstRowHBox.getChildren().add(imgViewCard);
           }
       }

      //This loop will add the three joker cards in second row
       //Here the uniqueness doesn't matter for the card
       for(int i=1;i<=3;i++) {
           //Below statement random.nextInt(2) will generate two random numbers 0 and 1 only as we are having
           //only two joker cards. Since two joker cards images number are 53.png and 54.png.
           //Hence adding 53 to get that correpsonding joker card number
           int randomNumber=random.nextInt(2)+53;

           //Creating ImageView object with the given card number image
           ImageView imgViewCard=new ImageView(new Image("file:C:\\Users\\JavaFXCards\\card"+randomNumber+".png"));

           //If the value of i is 1 i.e. it is first card then set the rotation angle as 45
           if(i==1)
               imgViewCard.setRotate(45);

           //If the value of i is 2 i.e. it is second card then set the rotation angle as 90
           if(i==2)
               imgViewCard.setRotate(90);

           //If the value of i is 3 i.e. it is third card then set the rotation angle as 135
           if(i==3)
               imgViewCard.setRotate(135);

           //Add the imgViewCard in secondRowHBox
           secondRowHBox.getChildren().add(imgViewCard);
       }

       //This loop will add the three more unique cards
       //Initializing cardNumber with 1
       int cardNumber=1;
       while(lstUnique52Cards.size()<6) {
           //Generate a randomNumber between 1 and 52 both inclusive
           //Since random.NextInt(52) will return number from 0 to 51 Hence adding 1 to
           //make it from 1 to 52
           int randomNumber=random.nextInt(52)+1;

           //If the current random generated is not present in the array list lstUnique52Cards
           //it means that the random number is unique then add that random number in array list lstUnique52Cards
           //then create the correpsonding ImageView with the card number represented by randomNumber
           //Also set the correpsonding angle to the cardNumber of this thirdRowHBox
           //Then add the image view card to the thirdRowHBox
           if(!lstUnique52Cards.contains(randomNumber)) {
               lstUnique52Cards.add(randomNumber);
               ImageView imgViewCard=new ImageView(new Image("file:C:\\Users\\JavaFXCards\\card"+randomNumber+".png"));
               if(cardNumber==1)
                   imgViewCard.setRotate(135);
               if(cardNumber==2)
                   imgViewCard.setRotate(90);
               if(cardNumber==3)
                   imgViewCard.setRotate(45);
               thirdRowHBox.getChildren().add(imgViewCard);
               cardNumber++; //Increment cardNumber by 1
           }
       }

       //Add all the three HBox objects in the vBox
       vBox.getChildren().add(firstRowHBox);
       vBox.getChildren().add(secondRowHBox);
       vBox.getChildren().add(thirdRowHBox);

       //Create a scene object with the child as vBox
       Scene scene = new Scene(vBox ,450, 450);

       //Setting the primaryStage title as Cards
       primaryStage.setTitle("Cards");

       //Setting the scene to the primaryStage
       primaryStage.setScene(scene);

       //Showing the primaryStage
       primaryStage.show();
   }

   //Main method it will invoke start method of Application class
   public static void main(String[] args) {
       launch(args);
   }

}