getImage()的路径问题，老是空指针，有谁可以帮看一下吗

问题遇到的现象和发生背景

这个是我的代码
```java
package game;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class MainFrame extends JFrame {

     Image bg=Toolkit.getDefaultToolkit().getImage("images/sky.jpg");
    
    
    
    private JPanel contentPane;
@Override
public void paint(Graphics g) {
    // TODO Auto-generated method stub
    super.paint(g);
    g.drawImage(bg, 0,0,null);
    
}
    
    


    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainFrame frame = new MainFrame();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    
    public MainFrame() {
        setFont(new Font("Bahnschrift", Font.PLAIN, 16));
        setBackground(Color.GRAY);
        setTitle("\u7BA1\u96EA\u51AC\u7684\u9EC4\u91D1\u77FF\u5DE5");
        paint(getGraphics());
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 790, 668);
        contentPane = new JPanel();
        contentPane.setForeground(Color.ORANGE);
        contentPane.setToolTipText("");
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);
        contentPane.addMouseListener(new MouseListener() {
            
            @Override
            public void mouseReleased(MouseEvent e) {
                // TODO Auto-generated method stub
                
            }
            
            @Override
            public void mousePressed(MouseEvent e) {
                // TODO Auto-generated method stub
                
            }
            
            @Override
            public void mouseExited(MouseEvent e) {
                // TODO Auto-generated method stub
                
            }
            
            @Override
            public void mouseEntered(MouseEvent e) {
                // TODO Auto-generated method stub
                
            }
            
            @Override
            public void mouseClicked(MouseEvent e) {
                // TODO Auto-generated method stub
                
            }
        });
    }
    }

    

这个是我的文件夹：

这个是我的运行框：

问题相关代码，请勿粘贴截图

用了相对路径和绝对路径都不行

错误是g为空，paint(getGraphics());
public void paint(Graphics g) {
super.paint(g);
g.drawImage(bg, 0,0,null);
｝

检查g

JAVA中传递的路径需要双斜杠，你看看路径有没有写错，