While compiling NetBeans source code with (jdk 1.4.2 b18) I got:

     Compiling 133 source files to /data/cvs/netbeans/trunk/nb_all/java/src
     An exception has occurred in the compiler (1.4.2-beta). Please file a bug at the Java Developer Connection (http://java.sun.com/cgi-bin/bugreport.cgi)  after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report.  Thank you.
     java.lang.NullPointerException
         at com.sun.tools.javac.v8.comp.Flow.checkInit(Flow.java:380)
         at com.sun.tools.javac.v8.comp.Flow.visitIdent(Flow.java:1131)
         at com.sun.tools.javac.v8.tree.Tree$Ident.accept(Tree.java:1111)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.tree.TreeScanner.visitSelect(TreeScanner.java:242)
         at com.sun.tools.javac.v8.tree.Tree$Select.accept(Tree.java:1091)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanExpr(Flow.java:501)
         at com.sun.tools.javac.v8.comp.Flow.visitBinary(Flow.java:1123)
         at com.sun.tools.javac.v8.tree.Tree$Binary.accept(Tree.java:1014)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:42)
         at com.sun.tools.javac.v8.tree.TreeScanner.visitNewArray(TreeScanner.java:200)
         at com.sun.tools.javac.v8.tree.Tree$NewArray.accept(Tree.java:922)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanExpr(Flow.java:501)
         at com.sun.tools.javac.v8.comp.Flow.visitVarDef(Flow.java:703)
         at com.sun.tools.javac.v8.tree.Tree$VarDef.accept(Tree.java:511)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanStat(Flow.java:483)
         at com.sun.tools.javac.v8.comp.Flow.scanStats(Flow.java:492)
         at com.sun.tools.javac.v8.comp.Flow.visitBlock(Flow.java:711)
         at com.sun.tools.javac.v8.tree.Tree$Block.accept(Tree.java:547)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanStat(Flow.java:483)
         at com.sun.tools.javac.v8.comp.Flow.visitIf(Flow.java:996)
         at com.sun.tools.javac.v8.tree.Tree$If.accept(Tree.java:756)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanStat(Flow.java:483)
         at com.sun.tools.javac.v8.comp.Flow.scanStats(Flow.java:492)
         at com.sun.tools.javac.v8.comp.Flow.visitBlock(Flow.java:711)
         at com.sun.tools.javac.v8.tree.Tree$Block.accept(Tree.java:547)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanStat(Flow.java:483)
         at com.sun.tools.javac.v8.comp.Flow.visitForLoop(Flow.java:793)
         at com.sun.tools.javac.v8.tree.Tree$ForLoop.accept(Tree.java:605)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanStat(Flow.java:483)
         at com.sun.tools.javac.v8.comp.Flow.scanStats(Flow.java:492)
         at com.sun.tools.javac.v8.comp.Flow.visitBlock(Flow.java:711)
         at com.sun.tools.javac.v8.tree.Tree$Block.accept(Tree.java:547)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.scanStat(Flow.java:483)
         at com.sun.tools.javac.v8.comp.Flow.visitMethodDef(Flow.java:665)
         at com.sun.tools.javac.v8.tree.Tree$MethodDef.accept(Tree.java:482)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.visitClassDef(Flow.java:615)
         at com.sun.tools.javac.v8.tree.Tree$ClassDef.accept(Tree.java:443)
         at com.sun.tools.javac.v8.tree.TreeScanner.scan(TreeScanner.java:33)
         at com.sun.tools.javac.v8.comp.Flow.analyzeTree(Flow.java:1156)
         at com.sun.tools.javac.v8.JavaCompiler.compile(JavaCompiler.java:361)
         at com.sun.tools.javac.v8.Main.compile(Main.java:569)
         at com.sun.tools.javac.Main.compile(Main.java:36)
         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
         at java.lang.reflect.Method.invoke(Method.java:324)
         at org.apache.tools.ant.taskdefs.compilers.Javac13.execute(Javac13.java:92)
         at org.apache.tools.ant.taskdefs.Javac.execute(Javac.java:557)
         at org.apache.tools.ant.Task.perform(Task.java:217)
         at org.apache.tools.ant.Target.execute(Target.java:184)
         at org.apache.tools.ant.Target.performTasks(Target.java:202)
         at org.apache.tools.ant.Project.executeTarget(Project.java:601)
         at org.apache.tools.ant.taskdefs.Ant.execute(Ant.java:266)
         at org.apache.tools.ant.Task.perform(Task.java:217)
         at org.apache.tools.ant.Target.execute(Target.java:184)
         at org.netbeans.nbbuild.NbMerge.FixedModulesBuild(Unknown Source)
         at org.netbeans.nbbuild.NbMerge.execute(Unknown Source)
         at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:104)
         at org.apache.tools.ant.Task.perform(Task.java:217)
         at org.apache.tools.ant.Target.execute(Target.java:184)
         at org.apache.tools.ant.Target.performTasks(Target.java:202)
         at org.apache.tools.ant.Project.executeTarget(Project.java:601)
         at org.apache.tools.ant.Project.executeTargets(Project.java:560)
         at org.apache.tools.ant.Main.runBuild(Main.java:454)
         at org.apache.tools.ant.Main.start(Main.java:153)
         at org.apache.tools.ant.Main.main(Main.java:176)