Exception occured when:
1) I have the source code (see below)
2) Hold Ctrl key
3) Get the mouse cursor over the "abcdef" text
4) wait a second to the hyperlink tooltip

Source code:
public class Midlet extends MIDlet {abcdef
}

Exception:
java.io.IOException
at org.netbeans.api.java.source.JavaSource.runUserActionTask(JavaSource.java:322)
[catch] at
org.netbeans.modules.editor.java.GoToSupport.performGoTo(GoToSupport.java:76)
at
org.netbeans.modules.editor.java.GoToSupport.getGoToElementTooltip(GoToSupport.java:67)
at
org.netbeans.modules.java.editor.hyperlink.JavaHyperlinkProvider.getShortDescription(JavaHyperlinkProvider.java:103)
at
org.netbeans.lib.editor.hyperlink.HyperlinkOperation$1.run(HyperlinkOperation.java:92)
at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:525)
at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:957)
Caused by: java.lang.NullPointerException
at
org.netbeans.api.java.source.SourceUtils.getEnclosingTypeElement(SourceUtils.java:225)
at
org.netbeans.modules.editor.java.GoToSupport$DisplayNameElementVisitor.visitType(GoToSupport.java:215)
at
org.netbeans.modules.editor.java.GoToSupport$DisplayNameElementVisitor.visitType(GoToSupport.java:171)
at com.sun.tools.javac.code.Symbol$ClassSymbol.accept(Symbol.java:827)
at
javax.lang.model.util.AbstractElementVisitor6.visit(AbstractElementVisitor6.java:68)
at org.netbeans.modules.editor.java.GoToSupport$1.run(GoToSupport.java:109)
at org.netbeans.modules.editor.java.GoToSupport$1.run(GoToSupport.java:79)
at org.netbeans.api.java.source.JavaSource.runUserActionTask(JavaSource.java:320)
... 6 more