Its impossible to add an "out-identifier" (which is pretty bad). The JSON Marshaller works fine, though. Can I get a clean implementation somewhere? Exception: Exception in thread "main" java.lang.NullPointerException at com.thoughtworks.xstream.io.xml.PrettyPrintWriter.writeText(PrettyPrintWriter.java:203) at com.thoughtworks.xstream.io.xml.PrettyPrintWriter.writeAttributeValue(PrettyPrintWriter.java:195) at com.thoughtworks.xstream.io.xml.PrettyPrintWriter.addAttribute(PrettyPrintWriter.java:190) at com.thoughtworks.xstream.io.WriterWrapper.addAttribute(WriterWrapper.java:41) at org.drools.runtime.help.impl.XStreamXML$InsertConverter.marshal(XStreamXML.java:119) at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:68) at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:78) at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:63) at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.writeItem(AbstractCollectionConverter.java:64) at com.thoughtworks.xstream.converters.collections.CollectionConverter.marshal(CollectionConverter.java:55) at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:68) at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:78) at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:63) at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$2.visit(AbstractReflectionConverter.java:115) at com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider.visitSerializableFields(PureJavaReflectionProvider.java:129) at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doMarshal(AbstractReflectionConverter.java:100) at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.marshal(AbstractReflectionConverter.java:58) at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:68) at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:78) at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:63) at com.thoughtworks.xstream.core.TreeMarshaller.start(TreeMarshaller.java:98) at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.marshal(AbstractTreeMarshallingStrategy.java:38) at com.thoughtworks.xstream.XStream.marshal(XStream.java:837) at com.thoughtworks.xstream.XStream.marshal(XStream.java:826) at com.thoughtworks.xstream.XStream.toXML(XStream.java:801) at com.thoughtworks.xstream.XStream.toXML(XStream.java:789) at olli.Main.main(Main.java:58) -- View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/Drools-Server-5-1-1-S... Sent from the Drools - User mailing list archive at Nabble.com.