获取异常：java.lang.IllegalArgumentException:无法添加到布局：约束必须是字符串（或null）

我正在实施一个类似浏览器的项目，我遇到了一个例外

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.Insets;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import chrriis.dj.nativeswing.swtimpl.NativeInterface;
import chrriis.dj.nativeswing.swtimpl.components.JWebBrowser;

public class WebPageDisplay extends JPanel{

    public WebPageDisplay() {  

         super(new BorderLayout());  
         try{
       JPanel webBrowserPanel = new JPanel(new BorderLayout());   
       // webBrowserPanel.setBorder(BorderFactory.createTitledBorder("Native Web Browser component"));   
        final JWebBrowser webBrowser = new JWebBrowser();   
        webBrowser.setBarsVisible(false);   
        webBrowser.setStatusBarVisible(true);   
        webBrowserPanel.add(webBrowser, BorderLayout.CENTER);   
        add(webBrowserPanel, BorderLayout.CENTER);
                    webBrowser.navigate("www.google.com");
        JScrollPane scrollPane = new JScrollPane();   
        Dimension preferredSize = scrollPane.getPreferredSize();   
        preferredSize.height += 20;   
        scrollPane.setPreferredSize(preferredSize);   
//      add(scrollPane, BorderLayout.NORTH);   
        add(scrollPane,new GridBagConstraints(0, 2, 2, 1, 1.0, 1.0, GridBagConstraints.CENTER, 
            GridBagConstraints.BOTH, new Insets(0, 0, 0, 0), 0, 0));   

         }catch(Exception e){
             e.printStackTrace();

        }
      }

    public static void main(String[] args){
        NativeInterface.open();

         SwingUtilities.invokeLater(new Runnable() {

              public void run() {

                 WebPageDisplay webDisplay = new WebPageDisplay();

              }

            });

    }
}

java.lang.IllegalArgumentException: cannot add to layout: constraint must be a string (or null)
    at java.awt.BorderLayout.addLayoutComponent(BorderLayout.java:409)
    at java.awt.Container.addImpl(Container.java:1074)
    at java.awt.Container.add(Container.java:927)
    at WebPageDisplay.<init>(PBXPageDisplay.java:35)
    at WebPageDisplay$1.run(PBXPageDisplay.java:51)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:677)
    at java.awt.EventQueue.access$000(EventQueue.java:85)
    at java.awt.EventQueue$1.run(EventQueue.java:638)
    at java.awt.EventQueue$1.run(EventQueue.java:636)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:647)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

这是个例外

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.Insets;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import chrriis.dj.nativeswing.swtimpl.NativeInterface;
import chrriis.dj.nativeswing.swtimpl.components.JWebBrowser;

public class WebPageDisplay extends JPanel{

    public WebPageDisplay() {  

         super(new BorderLayout());  
         try{
       JPanel webBrowserPanel = new JPanel(new BorderLayout());   
       // webBrowserPanel.setBorder(BorderFactory.createTitledBorder("Native Web Browser component"));   
        final JWebBrowser webBrowser = new JWebBrowser();   
        webBrowser.setBarsVisible(false);   
        webBrowser.setStatusBarVisible(true);   
        webBrowserPanel.add(webBrowser, BorderLayout.CENTER);   
        add(webBrowserPanel, BorderLayout.CENTER);
                    webBrowser.navigate("www.google.com");
        JScrollPane scrollPane = new JScrollPane();   
        Dimension preferredSize = scrollPane.getPreferredSize();   
        preferredSize.height += 20;   
        scrollPane.setPreferredSize(preferredSize);   
//      add(scrollPane, BorderLayout.NORTH);   
        add(scrollPane,new GridBagConstraints(0, 2, 2, 1, 1.0, 1.0, GridBagConstraints.CENTER, 
            GridBagConstraints.BOTH, new Insets(0, 0, 0, 0), 0, 0));   

         }catch(Exception e){
             e.printStackTrace();

        }
      }

    public static void main(String[] args){
        NativeInterface.open();

         SwingUtilities.invokeLater(new Runnable() {

              public void run() {

                 WebPageDisplay webDisplay = new WebPageDisplay();

              }

            });

    }
}

java.lang.IllegalArgumentException: cannot add to layout: constraint must be a string (or null)
    at java.awt.BorderLayout.addLayoutComponent(BorderLayout.java:409)
    at java.awt.Container.addImpl(Container.java:1074)
    at java.awt.Container.add(Container.java:927)
    at WebPageDisplay.<init>(PBXPageDisplay.java:35)
    at WebPageDisplay$1.run(PBXPageDisplay.java:51)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:677)
    at java.awt.EventQueue.access$000(EventQueue.java:85)
    at java.awt.EventQueue$1.run(EventQueue.java:638)
    at java.awt.EventQueue$1.run(EventQueue.java:636)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:647)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

java.lang.IllegalArgumentException:无法添加到布局：约束必须是字符串（或null）
位于java.awt.BorderLayout.addLayoutComponent（BorderLayout.java:409）
位于java.awt.Container.addImpl（Container.java:1074）
在java.awt.Container.add处（Container.java:927）
在WebPageDisplay。（PBXPageDisplay.java:35）
在WebPageDisplay$1.run（PBXPageDisplay.java:51）
在java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:209）中
位于java.awt.EventQueue.dispatchEventImpl（EventQueue.java:677）
在java.awt.EventQueue.access$000（EventQueue.java:85）
在java.awt.EventQueue$1.run（EventQueue.java:638）
在java.awt.EventQueue$1.run（EventQueue.java:636）
位于java.security.AccessController.doPrivileged（本机方法）
位于java.security.AccessControlContext$1.doIntersectionPrivilege（AccessControlContext.java:87）
位于java.awt.EventQueue.dispatchEvent（EventQueue.java:647）
位于java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:296）
位于java.awt.EventDispatchThread.PumpeEventsforFilter（EventDispatchThread.java:211）
位于java.awt.EventDispatchThread.PumpeEventsforHierarchy（EventDispatchThread.java:201）
位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:196）
位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:188）
在java.awt.EventDispatchThread.run处（EventDispatchThread.java:122）

如果未使用GridBagLayout，则不能使用GridBagConstraints。编译器告诉你这没有意义，我完全同意。

@developer:建议再次是——不要使用GridBagConstraints，因为当使用的布局不是GridBagLayout时，它们没有意义。我不知道这会让你困惑。以上是您的全部代码还是借用了其中的任何部分，因为这是我理解您的困惑的唯一方法。@developer:那么您现在明白我的建议了吗？你为什么试图在这里使用GridBagConstraints？我已经创建了一个窗口（在此我将显示一个网页），该窗口将再次放置在另一个窗口中。你的评论对我来说没有意义。请澄清，让我们看看