java.lang.AssertionError: c = LockStep.ListFrobber tree.sym = LockStep.ListFrobber tree = 
abstract class ListFrobber {
    
    ListFrobber() {
        super();
    }
    
    abstract void frob(List l);
}
   at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:3183)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3165)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3114)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3096)
   at com.sun.tools.javac.comp.Attr.visitClassDef(Attr.java:690)
   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:594)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:458)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
   at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:508)
   at com.sun.tools.javac.comp.Attr.visitNewClass(Attr.java:1790)
   at com.sun.tools.javac.tree.JCTree$JCNewClass.accept(JCTree.java:1380)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:458)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
   at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:477)
   at com.sun.tools.javac.comp.Attr.visitReturn(Attr.java:1350)
   at com.sun.tools.javac.tree.JCTree$JCReturn.accept(JCTree.java:1248)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:458)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
   at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:508)
   at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:524)
   at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:906)
   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:789)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:458)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
   at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:508)
   at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:821)
   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:676)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:458)
   at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431)
   at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:508)
   at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:3239)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3165)
   at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3096)
   at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1244)
   at com.sun.tools.javac.api.JavacTaskImpl$2.process(JavacTaskImpl.java:480)
   at com.sun.tools.javac.api.JavacTaskImpl$Filter.run(JavacTaskImpl.java:631)
   at com.sun.tools.javac.api.JavacTaskImpl.analyze(JavacTaskImpl.java:483)
   at org.netbeans.modules.java.source.indexing.MultiPassCompileWorker.compile(MultiPassCompileWorker.java:244)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer$1.run(JavaCustomIndexer.java:199)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer$1.run(JavaCustomIndexer.java:161)
   at org.netbeans.modules.java.source.usages.ClassIndexManager.prepareWriteLock(ClassIndexManager.java:120)
   at org.netbeans.modules.java.source.indexing.JavaCustomIndexer.index(JavaCustomIndexer.java:161)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor$2.run(Indexable.java:153)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater.runIndexer(RepositoryUpdater.java:256)
   at org.netbeans.modules.parsing.spi.indexing.Indexable$MyAccessor.index(Indexable.java:151)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doIndex(RepositoryUpdater.java:1824)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.access$1400(RepositoryUpdater.java:1563)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$2.run(RepositoryUpdater.java:1744)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work$2.run(RepositoryUpdater.java:1742)
   at org.netbeans.modules.parsing.impl.indexing.errors.TaskCache.refreshTransaction(TaskCache.java:460)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.index(RepositoryUpdater.java:1742)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.scanFiles(RepositoryUpdater.java:2111)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$FileListWork.getDone(RepositoryUpdater.java:2299)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Work.doTheWork(RepositoryUpdater.java:2159)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task._run(RepositoryUpdater.java:3830)
   at org.netbeans.modules.parsing.impl.indexing.RepositoryUpdater$Task.run(RepositoryUpdater.java:3769)
   at org.netbeans.modules.parsing.impl.TaskProcessor$CompilationJob.run(TaskProcessor.java:610)
   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 java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
   at java.lang.Thread.run(Thread.java:662)