NPE whilst adding image to JPanel

Question

Whenever I try to add an image to my JPanel I get an NPE. (The error is when I initialize a new ImageIcon!)

What I've tried:

• Class loader
• Main class's get resource
• '/' before path and without '/' before path

Code in main class:

public class Main {
    public static void main(String[] args) {
        GameWindow game = new GameWindow();

        game.setSize(1280, 720);
        game.center();

        game.addImage(new ImageIcon(Main.class.getResource("player.png")).getImage(), 0, 0);

        game.setVisible(true);
    }
}

Inside the engine GameWindow class:

public class GameWindow {
    private final JFrame frame = new JFrame("Game Window");
    private final JPanel board = new JPanel();

    public GameWindow() {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void addImage(Image image, int x, int y) {
        board.getGraphics().drawImage(image, x, y, null);
    }

    public void center() {
        frame.setLocationRelativeTo(null);
    }

    public void setVisible(boolean visible) {
        if (visible) {
            if (!board.isVisible()) {
                board.setVisible(true);
                frame.add(board);
            }
        }
        frame.setVisible(visible);
    }

    public void setSize(int x, int y) {
        frame.setSize(x, y);
    }
}

Here's what the file path looks like before building it into a JAR and running it. Any help would be appreciated, I've spent so long (1 day + 1/2) trying to find an answer.