java.lang.AssertionError: LetExpr is not part of a public API
   at com.sun.tools.javac.tree.JCTree$LetExpr.accept(JCTree.java:2092)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$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:1176)
   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$JCBlock.accept(JCTree.java:793)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$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:693)
   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$JCClassDecl.accept(JCTree.java:620)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:76)
   at org.netbeans.modules.java.source.usages.SourceAnalyzerFactory$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.OnePassCompileWorker.compile(OnePassCompileWorker.java:257)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer.index(JavaCustomIndexer.java:235)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor$2.run(Indexable.java:158)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater.runIndexer(RepositoryUpdater.java:267)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor.index(Indexable.java:156)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doIndex(RepositoryUpdater.java:2498)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.access$1500(RepositoryUpdater.java:2096)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$2.run(RepositoryUpdater.java:2405)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$2.run(RepositoryUpdater.java:2403)
   at org.netbeans.modules.parsing.impl.indexing.errors.TaskCache.refreshTransaction(TaskCache.java:544)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.index(RepositoryUpdater.java:2403)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.scanFiles(RepositoryUpdater.java:2915)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$FileListWork.getDone(RepositoryUpdater.java:3290)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doTheWork(RepositoryUpdater.java:3022)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task._run(RepositoryUpdater.java:5313)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.access$4800(RepositoryUpdater.java:4993)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$2$1.run(RepositoryUpdater.java:5238)
   at org.netbeans.modules.parsing.impl.RunWhenScanFinishedSupport.performScan(RunWhenScanFinishedSupport.java:96)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$2.call(RepositoryUpdater.java:5234)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task$2.call(RepositoryUpdater.java:5230)
   at org.netbeans.modules.masterfs.filebasedfs.utils.FileChangedManager.priorityIO(FileChangedManager.java:176)
   at org.netbeans.modules.masterfs.providers.ProvidedExtensions.priorityIO(ProvidedExtensions.java:360)
   at org.netbeans.modules.parsing.impl.Utilities.runPriorityIO(Utilities.java:74)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.run(RepositoryUpdater.java:5230)
   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$Task.run(RequestProcessor.java:1454)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2036)