java.util.ConcurrentModificationException: Index ObjectsByClasses has been modified since iterator was created.
        at org.netbeans.mdr.persistence.btreeimpl.btreeindex.BtreeListByKey$BtreeListByKeyIterator.checkModCount(BtreeListByKey.java:201)
        at org.netbeans.mdr.persistence.btreeimpl.btreeindex.BtreeListByKey$BtreeListByKeyIterator.hasNext(BtreeListByKey.java:126)
        at org.netbeans.mdr.storagemodel.LiveCollection$LiveIterator.hasNext(LiveCollection.java:185)
        at org.netbeans.mdr.handlers.CollectionWrapper$IteratorWrapper.hasNext(CollectionWrapper.java:141)
        at org.netbeans.modules.classmodel.ProjectModel.findPhysicalMetamodel(ProjectModel.java:176)
        at org.netbeans.modules.classmodel.ProjectModel.createPhysicalMetamodel(ProjectModel.java:199)
        at org.netbeans.modules.classmodel.ProjectModel.createCodebaseExtent(ProjectModel.java:343)
        at org.netbeans.modules.classmodel.ProjectModel.refreshFileSystems(ProjectModel.java:328)
        at org.netbeans.modules.classmodel.ProjectModel.createProjectModel(ProjectModel.java:113)
        at org.netbeans.modules.classmodel.ui.actions.CreateModelAction.performAction(CreateModelAction.java:52)
        at org.openide.util.actions.NodeAction.performAction(NodeAction.java:180)
        at org.openide.util.actions.NodeAction.actionPerformed(NodeAction.java:171)
        at org.netbeans.core.ModuleActions$1.run(ModuleActions.java:105)
[catch] at org.openide.util.Task.run(Task.java:152)
        at org.openide.util.RequestProcessor$ProcessorThread.run(Unknown Source)