java.lang.AssertionError: LetExpr is not part of a public API
   at com.sun.tools.javac.tree.JCTree$LetExpr.accept(JCTree.java:2094)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:308)
   at com.sun.source.util.TreeScanner.visitExpressionStatement(TreeScanner.java:240)
   at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1178)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:308)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.visitIf(TreeScanner.java:234)
   at com.sun.tools.javac.tree.JCTree$JCIf.accept(JCTree.java:1153)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:308)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:159)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:795)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:308)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.visitMethod(TreeScanner.java:142)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitMethod(SourceAnalyzerFactory.java:746)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitMethod(SourceAnalyzerFactory.java:308)
   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:695)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:308)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:80)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitClass(SourceAnalyzerFactory.java:693)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitClass(SourceAnalyzerFactory.java:308)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:622)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:308)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitCompilationUnit(SourceAnalyzerFactory.java:427)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.visitCompilationUnit(SourceAnalyzerFactory.java:308)
   at com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:490)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$UsagesVisitor.scan(SourceAnalyzerFactory.java:410)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$StorableAnalyzer.analyse(SourceAnalyzerFactory.java:147)
   at org.netbeans.modules.java.source.indexing.JavaParsingContext.analyze(JavaParsingContext.java:229)
   at org.netbeans.modules.java.source.indexing.MultiPassCompileWorker.compile(MultiPassCompileWorker.java:283)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer.index(JavaCustomIndexer.java:232)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor$2.run(Indexable.java:158)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater.runIndexer(RepositoryUpdater.java:259)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor.index(Indexable.java:156)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doIndex(RepositoryUpdater.java:2457)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.access$1500(RepositoryUpdater.java:2057)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$2.run(RepositoryUpdater.java:2364)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$2.run(RepositoryUpdater.java:2362)
   at org.netbeans.modules.parsing.impl.indexing.errors.TaskCache.refreshTransaction(TaskCache.java:541)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.index(RepositoryUpdater.java:2362)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$AbstractRootsWork.scanSource(RepositoryUpdater.java:4781)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$AbstractRootsWork.scanSources(RepositoryUpdater.java:4507)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$RootsWork.getDone(RepositoryUpdater.java:4210)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doTheWork(RepositoryUpdater.java:2959)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task._run(RepositoryUpdater.java:5194)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.access$4800(RepositoryUpdater.java:4886)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$2$1.run(RepositoryUpdater.java:5131)
   at org.netbeans.modules.parsing.impl.RunWhenScanFinishedSupport.performScan(RunWhenScanFinishedSupport.java:96)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$2.call(RepositoryUpdater.java:5127)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$2.call(RepositoryUpdater.java:5123)
   at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:176)
   at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:360)
   at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:72)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.run(RepositoryUpdater.java:5123)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
   at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
   at java.util.concurrent.FutureTask.run(FutureTask.java:138)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1452)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2032)