java.lang.NullPointerException
        at org.openide.nodes.Children$Info.useNodes(Children.java:1307)
        at org.openide.nodes.Children.refreshOrder(Children.java:1255)
        at org.openide.nodes.Children.refreshEntry(Children.java:1186)
        at org.openide.nodes.Children$Array.refreshImpl(Children.java:1440)
        at org.openide.nodes.Children$Array$1.run(Children.java:1456)
        at org.openide.util.Mutex.postRequest(Mutex.java:1251)
        at org.openide.util.Mutex.postWriteRequest(Mutex.java:582)
        at org.openide.nodes.Children$Array.refresh(Children.java:1454)
        at org.openide.nodes.Children$Array.add(Children.java:1501)
        at org.netbeans.modules.db.explorer.DatabaseNodeChildren.addSubNode(DatabaseNodeChildren.java:267)
        at org.netbeans.modules.db.explorer.DatabaseNodeChildren.createSubnode(DatabaseNodeChildren.java:281)
        at org.netbeans.modules.db.explorer.infos.RootNodeInfo.addConnectionNoConnect(RootNodeInfo.java:208)
        at org.netbeans.api.db.explorer.ConnectionManager.addConnection(ConnectionManager.java:139)
        at org.netbeans.modules.derby.api.DerbyDatabases.registerDatabase(DerbyDatabases.java:365)
        at org.netbeans.modules.derby.api.DerbyDatabases.createSampleDatabase(DerbyDatabases.java:282)
        at org.netbeans.modules.derby.Installer$RegisterJDKDerby.registerSampleDatabase(Installer.java:108)
        at org.netbeans.modules.derby.Installer$RegisterJDKDerby.run(Installer.java:87)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:561)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:986)