FULL PRODUCT VERSION :
java version "1.5.0_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_05-b05)
Java HotSpot(TM) Client VM (build 1.5.0_05-b05, mixed mode, sharing)


ADDITIONAL OS VERSION INFORMATION :
Linux bass 2.4.31 #9 Sun Jun 26 22:44:43 MSD 2005 i686 i686 i386 GNU/Linux
Linux desperado 2.6.13-suspend2-r4 #3 SMP Fri Sep 16 12:13:52 MSD 2005 i686 AMD Athlon(TM) XP 2400+ AuthenticAMD GNU/Linux
SunOS aldan 5.9 Generic_117171-17 sun4u sparc SUNW,Ultra-5_10
Windows XP

A DESCRIPTION OF THE PROBLEM :
A certain piece of code (attached below) involving inheritance and generics can't be compiled with javac: it reports an internal NullPointerException.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Just try to compile the code attached.

Important: the code should be organized into 2 packages (just like in the example atached). If you merge everything to a single package, you won't get any error.


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The code should be compiled cleanly.
ACTUAL -
Compiler crashes with an internal error.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
An exception has occurred in the compiler (1.5.0_05). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport)  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.code.Types$IsSameTypeFcn.visitClassType(Types.java:652)
        at com.sun.tools.javac.code.Type$ClassType.accept(Type.java:482)
        at com.sun.tools.javac.code.Types$IsSameTypeFcn.isSameType(Types.java:601)
        at com.sun.tools.javac.code.Types$IsSameTypeFcn.visitClassType(Types.java:674)
        at com.sun.tools.javac.code.Type$ClassType.accept(Type.java:482)
        at com.sun.tools.javac.code.Types$IsSameTypeFcn.isSameType(Types.java:601)
        at com.sun.tools.javac.code.Types.isSameType(Types.java:591)
        at com.sun.tools.javac.code.Types.covariantReturnType(Types.java:2645)
        at com.sun.tools.javac.code.Types.resultSubtype(Types.java:2607)
        at com.sun.tools.javac.code.Types.returnTypeSubstitutable(Types.java:2615)
        at com.sun.tools.javac.code.Symbol$MethodSymbol.overrides(Symbol.java:814)
        at com.sun.tools.javac.code.Symbol$MethodSymbol.implementation(Symbol.java:866)
        at com.sun.tools.javac.comp.Check.firstUndef(Check.java:1354)
        at com.sun.tools.javac.comp.Check.firstUndef(Check.java:1367)
        at com.sun.tools.javac.comp.Check.checkAllDefined(Check.java:1319)
        at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:2436)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:2406)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:2355)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:444)
        at com.sun.tools.javac.main.Main.compile(Main.java:592)
        at com.sun.tools.javac.main.Main.compile(Main.java:544)
        at com.sun.tools.javac.Main.compile(Main.java:67)
        at com.sun.tools.javac.Main.main(Main.java:52)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
---- BEGIN a/AbstractFoo.java ----
package a;

public class AbstractFoo {
	public class InnerFoo<T> {}
}
---- END a/AbstractFoo.java ----
---- BEGIN a/Bar.java ----
package a;

import a.AbstractFoo.InnerFoo;

public interface Bar {
	InnerFoo<String> getInnerFoo();
}
---- END a/Bar.java ----
---- BEGIN b/Foo.java ----
package b;

import a.*;

public final class Foo extends AbstractFoo implements Bar {
	public InnerFoo<String> getInnerFoo() {
		return null;
	}
}
---- END b/Foo.java ----
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
There're three possible workarounds:

either abandon generalization of an inner class: a.AbstractFoo.InnerFoo instead of a.AbstractFoo.InnerFoo<T>,

or declare inner class static (though it may be never referenced from the static context),

or move the descendant class (b.Foo) to the package where its superclass and superinterface reside (a).
.