java.lang.NullPointerException
        at org.netbeans.modules.project.ant.AntBasedProjectFactorySingleton.getProjectFor(AntBasedProjectFactorySingleton.java:230)
        at org.netbeans.spi.project.support.ant.SourcesHelper.getProject(SourcesHelper.java:465)
        at org.netbeans.spi.project.support.ant.SourcesHelper.remarkExternalRoots(SourcesHelper.java:523)
        at org.netbeans.spi.project.support.ant.SourcesHelper.registerExternalRoots(SourcesHelper.java:516)
        at org.netbeans.modules.java.j2seproject.J2SESources$2.run(J2SESources.java:163)
        at org.openide.util.Mutex.leaveImpl(Mutex.java:902)
        at org.openide.util.Mutex.leave(Mutex.java:835)
        at org.openide.util.Mutex.readAccess(Mutex.java:333)
        at org.openide.util.Mutex$1R.run(Mutex.java:1299)
        at org.netbeans.api.project.ProjectManager$2$1.run(ProjectManager.java:120)
        at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:120)
        at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:499)
        at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:215)
        at org.netbeans.api.project.ProjectManager$2.execute(ProjectManager.java:118)
        at org.openide.util.Mutex.doWrapperAccess(Mutex.java:1320)
        at org.openide.util.Mutex.readAccess(Mutex.java:320)
        at org.netbeans.api.project.ProjectManager.findProject(ProjectManager.java:241)
        at org.netbeans.modules.project.ui.OpenProjectList.URLs2Projects(OpenProjectList.java:906)
        at org.netbeans.modules.project.ui.OpenProjectList.access$600(OpenProjectList.java:123)
        at org.netbeans.modules.project.ui.OpenProjectList$LoadOpenProjects.loadOnBackground(OpenProjectList.java:318)
        at org.netbeans.modules.project.ui.OpenProjectList$LoadOpenProjects.run(OpenProjectList.java:274)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:561)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:986)