FULL PRODUCT VERSION :
java version "1.6.0_14"
Java(TM) SE Runtime Environment (build 1.6.0_14-b08)
Java HotSpot(TM) 64-Bit Server VM (build 14.0-b16, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
OpenSuSE 11.1
2.6.27.23-0.1-default #1 SMP 2009-05-26 17:02:05 -0400 x86_64 x86_64 x86_64 GNU/Linux

EXTRA RELEVANT SYSTEM CONFIGURATION :
core 2 duo, 4 gb ram

A DESCRIPTION OF THE PROBLEM :
trying to compile an application with java 1.6 fails (java 1.7 works).
You'll need Maven 2.2 or later. This may be a Maven issue, even though
the problem seems to be occurring in the Java compiler. 

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
hg clone -r e665c9abb232 http://bitbucket.org/gatoatigrado/sketch/

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
compile works
ACTUAL -
null pointer exception inside the compiler

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Failure executing javac, but could not parse the error:
An exception has occurred in the compiler (1.6.0_14). 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.comp.Check.checkCompatibleConcretes(Check.java:1215)
        at com.sun.tools.javac.comp.Check.checkCompatibleSupertypes(Check.java:1567)
        at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:2674)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:2628)
        at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:2564)
        at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1036)
        at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:765)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:730)
        at com.sun.tools.javac.main.Main.compile(Main.java:353)
        at com.sun.tools.javac.main.Main.compile(Main.java:279)
        at com.sun.tools.javac.main.Main.compile(Main.java:270)
        at com.sun.tools.javac.Main.compile(Main.java:87)
        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:597)
        at org.codehaus.plexus.compiler.javac.JavacCompiler.compileInProcess(JavacCompiler.java:420)
        at org.codehaus.plexus.compiler.javac.JavacCompiler.compile(JavacCompiler.java:141)
        at org.apache.maven.plugin.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:493)
        at org.apache.maven.plugin.CompilerMojo.execute(CompilerMojo.java:114)
        at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:483)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:678)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalWithLifecycle(DefaultLifecycleExecutor.java:540)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:519)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:371)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:332)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:181)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:356)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:137)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:362)
        at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:41)
        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:597)
        at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
        at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
        at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
        at org.codehaus.classworlds.Launcher.main(Launcher.java:375)

REPRODUCIBILITY :
This bug can be reproduced often.