java.lang.AssertionError: LetExpr is not part of a public API
   at com.sun.tools.javac.tree.JCTree$LetExpr.accept(JCTree.java:2414)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.visitExpressionStatement(TreeScanner.java:243)
   at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1300)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:162)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:916)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:162)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:916)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.visitForLoop(TreeScanner.java:181)
   at com.sun.tools.javac.tree.JCTree$JCForLoop.accept(JCTree.java:1011)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:162)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:916)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.visitWhileLoop(TreeScanner.java:173)
   at com.sun.tools.javac.tree.JCTree$JCWhileLoop.accept(JCTree.java:970)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:162)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:916)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.visitMethod(TreeScanner.java:144)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitMethod(SourceAnalyzerFactory.java:768)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitMethod(SourceAnalyzerFactory.java:293)
   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:798)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitClass(SourceAnalyzerFactory.java:715)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitClass(SourceAnalyzerFactory.java:293)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:717)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:293)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitCompilationUnit(SourceAnalyzerFactory.java:420)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitCompilationUnit(SourceAnalyzerFactory.java:293)
   at com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:551)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:77)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:403)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$StorableAnalyzer.analyse(SourceAnalyzerFactory.java:155)
   at org.netbeans.modules.java.source.indexing.JavaParsingContext.analyze(JavaParsingContext.java:231)
   at org.netbeans.modules.java.source.indexing.MultiPassCompileWorker.compile(MultiPassCompileWorker.java:300)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer.index(JavaCustomIndexer.java:246)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor$2.run(Indexable.java:161)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater.runIndexer(RepositoryUpdater.java:282)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor.index(Indexable.java:159)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doIndex(RepositoryUpdater.java:2601)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.access$1300(RepositoryUpdater.java:2066)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$1.run(RepositoryUpdater.java:2491)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$1.run(RepositoryUpdater.java:2489)
   at org.netbeans.modules.parsing.impl.indexing.errors.TaskCache.refreshTransaction(TaskCache.java:544)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.index(RepositoryUpdater.java:2489)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$AbstractRootsWork.scanSource(RepositoryUpdater.java:5190)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$AbstractRootsWork.scanSources(RepositoryUpdater.java:4899)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$RootsWork.getDone(RepositoryUpdater.java:4604)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doTheWork(RepositoryUpdater.java:3194)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task._run(RepositoryUpdater.java:5632)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.access$4800(RepositoryUpdater.java:5298)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$3$1.run(RepositoryUpdater.java:5557)
   at org.netbeans.modules.parsing.impl.RunWhenScanFinishedSupport.performScan(RunWhenScanFinishedSupport.java:96)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$3.call(RepositoryUpdater.java:5553)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$3.call(RepositoryUpdater.java:5549)
   at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:176)
   at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:360)
   at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:74)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.run(RepositoryUpdater.java:5549)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
   at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
   at java.util.concurrent.FutureTask.run(FutureTask.java:166)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1432)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2042)