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:140)
   at org.netbeans.modules.xml.text.TextEditorSupport$3.stateChanged(TextEditorSupport.java:247)
   at org.openide.text.CloneableEditorSupport.fireStateChangeEvent(CloneableEditorSupport.java:2340)
   at org.openide.text.CloneableEditorSupport.fireDocumentChange(CloneableEditorSupport.java:2323)
   at org.openide.text.CloneableEditorSupport.access$900(CloneableEditorSupport.java:129)
   at org.openide.text.CloneableEditorSupport$3.doRun(CloneableEditorSupport.java:701)
   at org.openide.text.CloneableEditorSupport$3.run(CloneableEditorSupport.java:689)
Caused: org.openide.util.RequestProcessor$SlowItem: task failed due to: java.util.ConcurrentModificationException
   at org.openide.util.RequestProcessor$Task.schedule(RequestProcessor.java:1445)
   at org.openide.text.CloneableEditorSupport.prepareDocument(CloneableEditorSupport.java:759)
   at org.openide.text.CloneableEditorSupport.openDocumentImpl(CloneableEditorSupport.java:915)
   at org.openide.text.CloneableEditorSupport.openDocumentCheckIOE(CloneableEditorSupport.java:897)
   at org.openide.text.CloneableEditorSupport.openDocument(CloneableEditorSupport.java:879)
   at org.openide.text.DataEditorSupport.openDocument(DataEditorSupport.java:590)
   at org.netbeans.modules.versioning.ui.diff.DiffSidebar.getText(DiffSidebar.java:1017)
   at org.netbeans.modules.versioning.ui.diff.DiffSidebar.getText(DiffSidebar.java:929)
   at org.netbeans.modules.versioning.ui.diff.DiffSidebar.access$1300(DiffSidebar.java:114)
   at org.netbeans.modules.versioning.ui.diff.DiffSidebar$RefreshDiffTask.fetchOriginalContent(DiffSidebar.java:887)
   at org.netbeans.modules.versioning.ui.diff.DiffSidebar$RefreshDiffTask.computeDiff(DiffSidebar.java:858)
   at org.netbeans.modules.versioning.ui.diff.DiffSidebar$RefreshDiffTask.run(DiffSidebar.java:843)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1404)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1984)