java错误

帮忙看一下这是什么错误，拜谢~

Exception in thread "main" java.lang.IllegalArgumentException: Argument cannot be null
at org.eclipse.swt.SWT.error(Unknown Source)
at org.eclipse.swt.SWT.error(Unknown Source)
at org.eclipse.swt.SWT.error(Unknown Source)
at org.eclipse.swt.graphics.ImageLoader.load(Unknown Source)
at org.eclipse.swt.graphics.ImageDataLoader.load(Unknown Source)
at org.eclipse.swt.graphics.ImageData.(Unknown Source)
at org.eclipse.swt.graphics.Image.(Unknown Source)
at B.UsingImage.main(UsingImage.java:22)

源代码如下：

package B;

import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Shell;

public class UsingImage {

public static void main(String[] args) {
    Display display = Display.getDefault();

    Shell shell = new Shell(display);
    shell.setSize(180, 150);

    shell.open();

    Image iconImage = display.getSystemImage(SWT.ICON_QUESTION);
    shell.setImage(iconImage);
    Image buttonImage = new Image(display, UsingImage.class
            .getResourceAsStream("buttonImage.gif"));

    Button button = new Button(shell, SWT.NONE);
    button.setBounds(10, 50, 140, 50);
    button.setImage(buttonImage);
    button.setText("Image Button");

    Label label = new Label(shell,SWT.NONE);
    label.setImage(buttonImage);
    label.setBounds(10,10,30,30);

    while (!shell.isDisposed()) {
        if (!display.readAndDispatch())
            display.sleep();
    }
    buttonImage.dispose();

    display.dispose();
}

}

buttonImage.gif 需要放在 classpath的路径下

第22行，参数不能为空。

22行，应该是buttonImage.gif文件没找到。

iconImage
这个获取的是null所以不对