Running A Simple GUI Program

I'm getting back into the swing of things with Java after using I'm asked to utilize a simple GUI in order to take in the starting data, I cannot seem to get this to work. I'm getting this error Exception in thread "main" java.lang.NullPointerException

at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at Input.buildPanel(Input.java:53)
at Input.<init>(Input.java:27)
at InputDemo.main(InputDemo.java:5)

I've created two classes

import javax.swing.*;
public class Input extends JFrame {
private JPanel panel;
private JLabel messageLabel;
private JLabel messageLabel1;
private JLabel messageLabel2;
private JTextField shiftHrs;

[code]....