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.html.parser.ElementsFactory$CommonOpenTag.removeChildren(ElementsFactory.java:432)
   at org.netbeans.modules.html.parser.ParseTreeBuilder.appendChildrenToNewParent(ParseTreeBuilder.java:496)
   at org.netbeans.modules.html.parser.ParseTreeBuilder.appendChildrenToNewParent(ParseTreeBuilder.java:77)
   at nu.validator.htmlparser.impl.TreeBuilder.adoptionAgencyEndTag(TreeBuilder.java:4484)
   at nu.validator.htmlparser.impl.TreeBuilder.startTag(TreeBuilder.java:1936)
   at org.netbeans.modules.html.parser.ParseTreeBuilder.startTag(ParseTreeBuilder.java:388)
   at nu.validator.htmlparser.impl.Tokenizer.emitCurrentTagToken(Tokenizer.java:1136)
   at nu.validator.htmlparser.impl.Tokenizer.stateLoop(Tokenizer.java:2070)
   at nu.validator.htmlparser.impl.Tokenizer.tokenizeBuffer(Tokenizer.java:1331)
   at nu.validator.htmlparser.io.Driver.runStates(Driver.java:300)
   at nu.validator.htmlparser.io.Driver.tokenize(Driver.java:216)
   at org.netbeans.modules.html.parser.Html5Parser.parse(Html5Parser.java:129)
   at org.netbeans.modules.html.editor.lib.api.SyntaxAnalyzerResult.doParseHtml(SyntaxAnalyzerResult.java:245)
   at org.netbeans.modules.html.editor.lib.api.SyntaxAnalyzerResult.parseHtml(SyntaxAnalyzerResult.java:166)
   at org.netbeans.modules.html.editor.completion.HtmlCompletionQuery.query(HtmlCompletionQuery.java:212)
   at org.netbeans.modules.html.editor.completion.HtmlCompletionQuery$1.run(HtmlCompletionQuery.java:140)
   at org.netbeans.editor.BaseDocument.render(BaseDocument.java:1343)
   at org.netbeans.modules.html.editor.completion.HtmlCompletionQuery.run(HtmlCompletionQuery.java:133)
   at org.netbeans.modules.parsing.impl.TaskProcessor.callUserTask(TaskProcessor.java:583)
   at org.netbeans.modules.parsing.api.ParserManager$UserTaskAction.run(ParserManager.java:150)
   at org.netbeans.modules.parsing.api.ParserManager$UserTaskAction.run(ParserManager.java:134)
   at org.netbeans.modules.parsing.impl.TaskProcessor$2.call(TaskProcessor.java:200)
   at org.netbeans.modules.parsing.impl.TaskProcessor$2.call(TaskProcessor.java:197)
   at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:168)
   at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:360)
   at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:72)
Caused: org.netbeans.modules.parsing.spi.ParseException
   at org.netbeans.modules.parsing.impl.TaskProcessor.runUserTask(TaskProcessor.java:205)
   at org.netbeans.modules.parsing.api.ParserManager.parse(ParserManager.java:102)
   at org.netbeans.modules.html.editor.completion.HtmlCompletionQuery.query(HtmlCompletionQuery.java:116)
   at org.netbeans.modules.html.editor.completion.HtmlCompletionProvider$DocQuery.doQuery(HtmlCompletionProvider.java:218)
   at org.netbeans.modules.html.editor.completion.HtmlCompletionProvider$AbstractQuery.query(HtmlCompletionProvider.java:249)
   at org.netbeans.spi.editor.completion.support.AsyncCompletionTask.run(AsyncCompletionTask.java:223)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1452)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2032)