java.lang.AssertionError: Null members closure returned for symbol: java.util.Comparator of type: java.util.Comparator
   at com.sun.tools.javac.util.Assert.error(Assert.java:133)
   at com.sun.tools.javac.util.Assert.checkNonNull(Assert.java:118)
   at com.sun.tools.javac.code.Types$DescriptorCache.findDescriptorInternal(Types.java:410)
   at com.sun.tools.javac.code.Types$DescriptorCache.get(Types.java:391)
   at com.sun.tools.javac.code.Types.findDescriptorSymbol(Types.java:560)
   at com.sun.tools.javac.comp.Check.checkFunctionalInterface(Check.java:3648)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4466)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4389)
   at com.sun.tools.javac.comp.Attr.attrib(Attr.java:4364)
   at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1317)
   at com.sun.tools.javac.api.JavacTaskImpl$1.process(JavacTaskImpl.java:473)
   at com.sun.tools.javac.api.JavacTaskImpl$Filter.run(JavacTaskImpl.java:623)
   at com.sun.tools.javac.api.JavacTaskImpl.analyze(JavacTaskImpl.java:476)
   at org.netbeans.modules.java.source.TreeLoader.loadTreeFor(TreeLoader.java:199)
   at com.sun.tools.javac.model.JavacElements.getTreeAndTopLevel(JavacElements.java:588)
   at com.sun.tools.javac.model.JavacElements.getTreeAndTopLevel(JavacElements.java:614)
   at com.sun.tools.javac.api.JavacTrees.getPath(JavacTrees.java:331)
   at com.sun.tools.javac.api.JavacTrees.getPath(JavacTrees.java:323)
   at org.netbeans.modules.java.hints.SideEffectVisitor.visitMethodInvocation(SideEffectVisitor.java:216)
   at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1483)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at com.sun.source.util.TreeScanner.visitBinary(TreeScanner.java:322)
   at com.sun.tools.javac.tree.JCTree$JCBinary.accept(JCTree.java:1801)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:50)
   at org.netbeans.modules.java.hints.bugs.AssertWithSideEffects.run(AssertWithSideEffects.java:106)
   at sun.reflect.GeneratedMethodAccessor163.invoke(GeneratedMethodAccessor163.java:0)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.lang.reflect.Method.invoke(Method.java:497)
   at org.netbeans.modules.java.hints.providers.code.CodeHintProviderImpl$WorkerImpl.createErrors(CodeHintProviderImpl.java:339)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.runHint(HintsInvoker.java:810)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.access$400(HintsInvoker.java:112)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.runAndAdd(HintsInvoker.java:669)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:688)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:103)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:162)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:924)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.visitMethod(TreeScanner.java:144)
   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:806)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:103)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:99)
   at com.sun.source.util.TreeScanner.visitClass(TreeScanner.java:133)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:725)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.visitNewClass(TreeScanner.java:280)
   at com.sun.tools.javac.tree.JCTree$JCNewClass.accept(JCTree.java:1538)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.visitReturn(TreeScanner.java:255)
   at com.sun.tools.javac.tree.JCTree$JCReturn.accept(JCTree.java:1396)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:103)
   at com.sun.source.util.TreeScanner.visitBlock(TreeScanner.java:162)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:924)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.visitMethod(TreeScanner.java:144)
   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:806)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:103)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:99)
   at com.sun.source.util.TreeScanner.visitClass(TreeScanner.java:133)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:725)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:81)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:103)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:99)
   at com.sun.source.util.TreeScanner.visitClass(TreeScanner.java:133)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:725)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:68)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:94)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:694)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:622)
   at com.sun.source.util.TreeScanner.scan(TreeScanner.java:91)
   at org.netbeans.api.java.source.support.CancellableTreePathScanner.scan(CancellableTreePathScanner.java:103)
   at com.sun.source.util.TreeScanner.scanAndReduce(TreeScanner.java:99)
   at com.sun.source.util.TreeScanner.visitCompilationUnit(TreeScanner.java:120)
   at com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:551)
   at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:50)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker$ScannerImpl.scan(HintsInvoker.java:713)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.computeHintsImpl(HintsInvoker.java:257)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.computeHints(HintsInvoker.java:240)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.computeHints(HintsInvoker.java:210)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.computeHints(HintsInvoker.java:183)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsInvoker.computeHints(HintsInvoker.java:150)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsTask.run(HintsTask.java:137)
   at org.netbeans.modules.java.hints.spiimpl.hints.HintsTask.run(HintsTask.java:88)
   at org.netbeans.modules.java.source.JavaSourceAccessor$CancelableTaskWrapper.run(JavaSourceAccessor.java:298)
   at org.netbeans.modules.parsing.impl.TaskProcessor.callParserResultTask(TaskProcessor.java:584)
   at org.netbeans.modules.parsing.impl.TaskProcessor$RequestPerformer.run(TaskProcessor.java:809)
   at org.openide.util.lookup.Lookups.executeWith(Lookups.java:304)
   at org.netbeans.modules.parsing.impl.TaskProcessor$RequestPerformer.execute(TaskProcessor.java:725)
   at org.netbeans.modules.parsing.impl.TaskProcessor$CompilationJob.run(TaskProcessor.java:686)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
   at java.util.concurrent.FutureTask.run(FutureTask.java:266)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443)
   at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68)
   at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058)