java.util.ConcurrentModificationException
        at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
        at java.util.AbstractList$Itr.next(AbstractList.java:343)
        at org.netbeans.modules.xml.sync.DataObjectSyncSupport.addRepresentation(DataObjectSyncSupport.java:137)
        at org.netbeans.modules.xml.text.TextEditorSupport$3.stateChanged(TextEditorSupport.java:201)
        at org.openide.text.CloneableEditorSupport.fireStateChangeEvent(CloneableEditorSupport.java:2330)
        at org.openide.text.CloneableEditorSupport.fireDocumentChange(CloneableEditorSupport.java:2313)
        at org.openide.text.CloneableEditorSupport.access$900(CloneableEditorSupport.java:123)
        at org.openide.text.CloneableEditorSupport$3.doRun(CloneableEditorSupport.java:661)
        at org.openide.text.CloneableEditorSupport$3.run(CloneableEditorSupport.java:649)
Caused: org.openide.util.RequestProcessor$SlowItem: task failed due to: java.util.ConcurrentModificationException
        at org.openide.util.RequestProcessor$Task.schedule(RequestProcessor.java:655)
        at org.openide.text.CloneableEditorSupport.prepareDocument(CloneableEditorSupport.java:715)
        at org.openide.text.CloneableEditorSupport.openDocumentImpl(CloneableEditorSupport.java:850)
        at org.openide.text.CloneableEditorSupport.openDocumentCheckIOE(CloneableEditorSupport.java:832)
        at org.openide.text.CloneableEditorSupport.openDocument(CloneableEditorSupport.java:814)
        at org.openide.text.DataEditorSupport.openDocument(DataEditorSupport.java:493)
        at org.netbeans.modules.versioning.diff.DiffSidebar.getText(DiffSidebar.java:967)
        at org.netbeans.modules.versioning.diff.DiffSidebar.getText(DiffSidebar.java:874)
        at org.netbeans.modules.versioning.diff.DiffSidebar.access$1200(DiffSidebar.java:99)
        at org.netbeans.modules.versioning.diff.DiffSidebar$RefreshDiffTask.fetchOriginalContent(DiffSidebar.java:832)
        at org.netbeans.modules.versioning.diff.DiffSidebar$RefreshDiffTask.computeDiff(DiffSidebar.java:803)
        at org.netbeans.modules.versioning.diff.DiffSidebar$RefreshDiffTask.run(DiffSidebar.java:793)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:602)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1084)