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:2297)
        at org.openide.text.CloneableEditorSupport.fireDocumentChange(CloneableEditorSupport.java:2280)
        at org.openide.text.CloneableEditorSupport.access$1100(CloneableEditorSupport.java:122)
        at org.openide.text.CloneableEditorSupport$2.doRun(CloneableEditorSupport.java:622)
        at org.openide.text.CloneableEditorSupport$2.run(CloneableEditorSupport.java:610)
Caused: org.openide.util.RequestProcessor$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:675)
        at org.openide.text.CloneableEditorSupport.openDocumentImpl(CloneableEditorSupport.java:810)
        at org.openide.text.CloneableEditorSupport.openDocumentCheckIOE(CloneableEditorSupport.java:792)
        at org.openide.text.CloneableEditorSupport.openDocument(CloneableEditorSupport.java:774)
        at org.openide.text.DataEditorSupport.openDocument(DataEditorSupport.java:489)
        at org.netbeans.modules.versioning.diff.DiffSidebar.getText(DiffSidebar.java:960)
        at org.netbeans.modules.versioning.diff.DiffSidebar.getText(DiffSidebar.java:867)
        at org.netbeans.modules.versioning.diff.DiffSidebar.access$1100(DiffSidebar.java:97)
        at org.netbeans.modules.versioning.diff.DiffSidebar$RefreshDiffTask.fetchOriginalContent(DiffSidebar.java:825)
        at org.netbeans.modules.versioning.diff.DiffSidebar$RefreshDiffTask.computeDiff(DiffSidebar.java:796)
        at org.netbeans.modules.versioning.diff.DiffSidebar$RefreshDiffTask.run(DiffSidebar.java:786)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:602)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1084)