when the program is executed, it has an error, and I don't know what to fix.

The error shows like this:

Exception in Application start method

java.lang.reflect.InvocationTargetException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:498)

at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)

at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:498)

at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)

Caused by: java.lang.RuntimeException: Exception in Application start method

at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)

at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$154(LauncherImpl.java:182)

at java.lang.Thread.run(Thread.java:748)

Caused by: java.lang.NullPointerException

at javafx.scene.layout.Pane.setConstraint(Pane.java:103)

at javafx.scene.layout.GridPane.setRowIndex(GridPane.java:296)

at javafx.scene.layout.GridPane.setConstraints(GridPane.java:553)

at javafx.scene.layout.GridPane.add(GridPane.java:964)

at q5.EmailPane.(EmailPane.java:98)

at q5.Email.start(Email.java:26)

at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)

at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)

at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)

at java.security.AccessController.doPrivileged(Native Method)

at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)

at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)

Exception running application q5.Email

This is the program:

package q5;

import javafx.application.Application;

import javafx.scene.Scene;

import javafx.stage.Stage;

public class Email extends Application {

/**

* Launches the email application.

*

* @param primaryStage

* a Stage

*/

public void start(Stage primaryStage) {

final int appWidth = 700; // width of the pop-up window.

final int appHeight = 500; // height of the pop-up window.

Scene scene = new Scene(new EmailPane(), appWidth, appHeight);

primaryStage.setTitle("Email"); // title of the window.

primaryStage.setScene(scene);

primaryStage.show();

}

/**

* Launches the JavaFX application.

*

* @param args

* command line arguments

*/

public static void main(String[] args) {

launch(args);

}

}