This is a problem in the prototype for jsr14 generics:

frog$ cat -n T.java
     1 class T {
     2 public static <S, T extends S> void f(S s, T t) {}
     3 }
frog$ /java/jdk/ws/tools/jsr14/build/solaris-sparc/bin/javac -gj T.java
T.java:2: unexpected type
found : S
required: class
    public static <S, T extends S> void f(S s, T t) {}
                                ^
An exception has occurred in the compiler (1.4.0-internal). 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.code.Type$TypeVar.supertype(Type.java:1264)
        at com.sun.tools.javac.v8.comp.Check.checkClassBounds(Check.java:1041)
        at com.sun.tools.javac.v8.comp.Check.checkClassBounds(Check.java:1018)
        at com.sun.tools.javac.v8.comp.Check$Validator._case(Check.java:521)
        at com.sun.tools.javac.v8.tree.Tree$TypeParameter.visit(Tree.java:979)
        at com.sun.tools.javac.v8.comp.Check.validate(Check.java:460)
        at com.sun.tools.javac.v8.comp.Check.validateTypeParams(Check.java:478)
        at com.sun.tools.javac.v8.comp.Attr._case(Attr.java:419)
        at com.sun.tools.javac.v8.tree.Tree$MethodDef.visit(Tree.java:416)
        at com.sun.tools.javac.v8.comp.Attr.attribTree(Attr.java:274)
        at com.sun.tools.javac.v8.comp.Attr.attribStat(Attr.java:308)
        at com.sun.tools.javac.v8.comp.Attr.attribClass(Attr.java:2000)
        at com.sun.tools.javac.v8.JavaCompiler.compile(JavaCompiler.java:375)
        at com.sun.tools.javac.v8.Main.compile(Main.java:411)
        at com.sun.tools.javac.Main.compile(Main.java:28)
        at com.sun.tools.javac.Main.main(Main.java:19)
frog$