Error: JavaFX runtime components are missing, and are required to run this application. run the project with gradle

I am building a java project in intellij. I alreadly imported the gradle script and build.gradle file can be successfully built. However, when I ran my java files, this error occurs: "JavaFX runtime components are missing, and are required to run this application". I am really not sure what is the issue.
This is my Main.java file:

This is the launcher

and this is the Duke.java files:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ScrollPane;
import javafx.scene.control.TextField;
import javafx.scene.image.Image;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.Region;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import static java.lang.Integer.parseInt;
public class Duke extends Application {
private Storage storage;
private TaskList tasks;
private Ui ui;
private ScrollPane scrollPane;
private VBox dialogContainer;
private TextField userInput;
private Button sendButton;
private Scene scene;
private Image user = new Image(this.getClass().getResourceAsStream("images/DaUser.png"));
private Image duke = new Image(this.getClass().getResourceAsStream("images/DaDuke.png"));
@Override
public void start(Stage stage) {
//Step 1. Setting up required components
//The container for the content of the chat to scroll.
scrollPane = new ScrollPane();
dialogContainer = new VBox();
scrollPane.setContent(dialogContainer);
userInput = new TextField();
sendButton = new Button("Send");
AnchorPane mainLayout = new AnchorPane();
mainLayout.getChildren().addAll(scrollPane, userInput, sendButton);
scene = new Scene(mainLayout);
stage.setScene(scene);
stage.show();
stage.setTitle("Duke");
stage.setResizable(false);
stage.setMinHeight(600.0);
stage.setMinWidth(400.0);
mainLayout.setPrefSize(400.0, 600.0);
scrollPane.setPrefSize(385, 535);
scrollPane.setHbarPolicy(ScrollPane.ScrollBarPolicy.NEVER);
scrollPane.setVbarPolicy(ScrollPane.ScrollBarPolicy.ALWAYS);
scrollPane.setVvalue(1.0);
scrollPane.setFitToWidth(true);
// You will need to import `javafx.scene.layout.Region` for this.
dialogContainer.setPrefHeight(Region.USE_COMPUTED_SIZE);
userInput.setPrefWidth(325.0);
sendButton.setPrefWidth(55.0);
AnchorPane.setTopAnchor(scrollPane, 1.0);
AnchorPane.setBottomAnchor(sendButton, 1.0);
AnchorPane.setRightAnchor(sendButton, 1.0);
AnchorPane.setLeftAnchor(userInput, 1.0);
AnchorPane.setBottomAnchor(userInput, 1.0);
sendButton.setOnMouseClicked((event) -> {
handleUserInput();
});
userInput.setOnAction((event) -> {
handleUserInput();
});
dialogContainer.heightProperty().addListener((observable) -> scrollPane.setVvalue(1.0));
}
private void handleUserInput() {
Label userText = new Label(userInput.getText());
Label dukeText = new Label(getResponse(userInput.getText()));
dialogContainer.getChildren().addAll(
DialogBox.getUserDialog(userText.getText(), user),
DialogBox.getDukeDialog(dukeText.getText(), duke)
);
userInput.clear();
}
public String getResponse(String input) {
return "Duke heard: " + input;
}
public Duke(String filePath) {
ui = new Ui();
storage = new Storage(filePath);
try {
tasks = new TaskList(storage.load());
} catch (DukeException e) {
ui.showLoadingError();
tasks = new TaskList();
}
}
public Duke() {
this("data/duke.txt");
}
public static void main(String[] args) {
new Duke("data/duke.txt").run();
}
public void run() {
ui.showWelcome();
boolean isExit = false;
while (!isExit) {
try {
String fullCommand = ui.readCommand();
ui.showLine(); 
Command c = Parser.parse(fullCommand);
c.execute(tasks, ui, storage);
isExit = c.isExit();
} catch (DukeException e) {
ui.showError(e.getMessage());
} finally {
ui.showLine();
}
}
}
}

update: I imported the lib folder into my project and now the error is gone. But another error occurs when I ran the project, which is "Caused by: java.lang.NullPointerException: Input stream must not be null"

According to your comment you are using Java 13 and not Java 11.

JavaFX is not part of the JDK in Java 13 and also not in Java 11. You can get JavaFX from openjfx.io. Then you need to add the JavaFX JAR files to your module path because since JDK 9, java uses modules.

Unrelated to your question, but the "system" properties contain details about the java version, for example...

System.getProperty("java.runtime.version");