I have added the jpamodelgen as annotation processor to an ejb project. However, when recompiling, not all meta classes are created. The processor crashes with a NPE. Compiling the project with the same jdk and ant works fine.

java.lang.NullPointerException
at org.eclipse.jdt.apt.core.internal.AptCompilationParticipant.addJava6GeneratedFile(AptCompilationParticipant.java:272)
at org.eclipse.jdt.internal.apt.pluggable.core.dispatch.IdeProcessingEnvImpl.addNewUnit(IdeProcessingEnvImpl.java:132)
at org.eclipse.jdt.internal.apt.pluggable.core.filer.IdeJavaSourceOutputStream.close(IdeJavaSourceOutputStream.java:72)
at sun.nio.cs.StreamEncoder.implClose(StreamEncoder.java:320)
at sun.nio.cs.StreamEncoder.close(StreamEncoder.java:149)
at java.io.OutputStreamWriter.close(OutputStreamWriter.java:233)
at java.io.BufferedWriter.close(BufferedWriter.java:266)
at java.io.PrintWriter.close(PrintWriter.java:339)
at org.hibernate.jpamodelgen.ClassWriter.writeFile(ClassWriter.java:80)
at org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor.createMetaModelClasses(JPAMetaModelEntityProcessor.java:155)
at org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor.process(JPAMetaModelEntityProcessor.java:145)
at org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.handleProcessor(RoundDispatcher.java:139)
at org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.round(RoundDispatcher.java:121)
at org.eclipse.jdt.internal.compiler.apt.dispatch.BaseAnnotationProcessorManager.processAnnotations(BaseAnnotationProcessorManager.java:159)
at org.eclipse.jdt.internal.apt.pluggable.core.dispatch.IdeAnnotationProcessorManager.processAnnotations(IdeAnnotationProcessorManager.java:134)
at org.eclipse.jdt.internal.compiler.Compiler.processAnnotations(Compiler.java:820)
at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:434)
at org.eclipse.jdt.internal.core.builder.AbstractImageBuilder.compile(AbstractImageBuilder.java:365)
at org.eclipse.jdt.internal.core.builder.BatchImageBuilder.compile(BatchImageBuilder.java:178)
at org.eclipse.jdt.internal.core.builder.AbstractImageBuilder.compile(AbstractImageBuilder.java:302)
at org.eclipse.jdt.internal.core.builder.BatchImageBuilder.build(BatchImageBuilder.java:60)
at org.eclipse.jdt.internal.core.builder.JavaBuilder.buildAll(JavaBuilder.java:254)
at org.eclipse.jdt.internal.core.builder.JavaBuilder.build(JavaBuilder.java:173)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:726)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:199)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:239)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:292)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:295)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:351)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:374)
at org.eclipse.core.internal.resources.Workspace.buildInternal(Workspace.java:513)
at org.eclipse.core.internal.resources.Workspace.build(Workspace.java:422)
at org.eclipse.ui.actions.GlobalBuildAction$1.run(GlobalBuildAction.java:180)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)