java.lang.AssertionError: LetExpr is not part of a public API
   at com.sun.tools.javac.tree.JCTree$LetExpr.accept(JCTree.java:2397)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.visitExpressionStatement(TreeScanner.java:241)
   at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1284)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:160)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:900)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.visitForLoop(TreeScanner.java:179)
   at com.sun.tools.javac.tree.JCTree$JCForLoop.accept(JCTree.java:995)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:160)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:900)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.visitForLoop(TreeScanner.java:179)
   at com.sun.tools.javac.tree.JCTree$JCForLoop.accept(JCTree.java:995)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:160)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:900)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.visitMethod(TreeScanner.java:143)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitMethod(SourceAnalyzerFactory.java:767)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitMethod(SourceAnalyzerFactory.java:292)
   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:800)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitClass(SourceAnalyzerFactory.java:714)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitClass(SourceAnalyzerFactory.java:292)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:719)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:292)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitCompilationUnit(SourceAnalyzerFactory.java:419)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitCompilationUnit(SourceAnalyzerFactory.java:292)
   at com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:553)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:402)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$StorableAnalyzer.analyse(SourceAnalyzerFactory.java:154)
   at org.netbeans.modules.java.source.indexing.JavaParsingContext.analyze(JavaParsingContext.java:228)
   at org.netbeans.modules.java.source.indexing.MultiPassCompileWorker.compile(MultiPassCompileWorker.java:289)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer.index(JavaCustomIndexer.java:236)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor$2.run(Indexable.java:161)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater.runIndexer(RepositoryUpdater.java:266)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor.index(Indexable.java:159)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doIndex(RepositoryUpdater.java:2472)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.access$1200(RepositoryUpdater.java:2040)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$1.run(RepositoryUpdater.java:2364)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$1.run(RepositoryUpdater.java:2362)
   at org.netbeans.modules.parsing.impl.indexing.errors.TaskCache.refreshTransaction(TaskCache.java:544)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.index(RepositoryUpdater.java:2362)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.scanFiles(RepositoryUpdater.java:2943)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$FileListWork.getDone(RepositoryUpdater.java:3396)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doTheWork(RepositoryUpdater.java:3059)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task._run(RepositoryUpdater.java:5476)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.access$4600(RepositoryUpdater.java:5142)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$3$1.run(RepositoryUpdater.java:5401)
   at org.netbeans.modules.parsing.impl.RunWhenScanFinishedSupport.performScan(RunWhenScanFinishedSupport.java:96)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$3.call(RepositoryUpdater.java:5397)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$3.call(RepositoryUpdater.java:5393)
   at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:176)
   at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:360)
   at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:74)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.run(RepositoryUpdater.java:5393)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
   at java.util.concurrent.FutureTask.run(FutureTask.java:262)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1432)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2044)