nullpointerexception - NullPointerException 我不明白

Question

我是一名初级 Java 程序员，运行我的程序时出现此异常，该异常太长而无法在此处发布，有人可以解释此堆栈跟踪...谢谢！

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.text.BoxView.calculateMinorAxisRequirements(Unknown Source)
    at javax.swing.text.html.BlockView.calculateMinorAxisRequirements(Unknown Source)
    at javax.swing.text.BoxView.checkRequests(Unknown Source)
    at javax.swing.text.BoxView.getMinimumSpan(Unknown Source)
    at javax.swing.text.html.BlockView.getMinimumSpan(Unknown Source)
    at javax.swing.plaf.basic.BasicTextUI$RootView.getMinimumSpan(Unknown Source)
    at javax.swing.plaf.basic.BasicTextUI.getMinimumSize(Unknown Source)
    at javax.swing.JEditorPane.getScrollableTracksViewportWidth(Unknown Source)
    at javax.swing.JEditorPane.getPreferredSize(Unknown Source)
    at javax.swing.ScrollPaneLayout.layoutContainer(Unknown Source)
    at java.awt.Container.layout(Unknown Source)
    at java.awt.Container.doLayout(Unknown Source)
    at java.awt.Container.validateTree(Unknown Source)
    at java.awt.Container.validate(Unknown Source)
    at javax.swing.RepaintManager.validateInvalidComponents(Unknown Source)
    at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)