Problem with XmlJavaTypeAdapter

When i try to create the documentation for the class https://bitbucket.org/sdorra/scm-manager/src/tip/scm-core/src/main/java/sonia/scm/config/ScmConfiguration.java i get the following exception:

Caused by: org.codehaus.enunciate.contract.validation.ValidationException: (unknown source position): adminGroups: adapter sonia.scm.xml.XmlSetStringAdapter does not adapt java.lang.String
at org.codehaus.enunciate.contract.jaxb.adapters.AdapterUtil.findAdapterType(AdapterUtil.java:134)
at org.codehaus.enunciate.contract.jaxb.adapters.AdapterUtil.findAdapterType(AdapterUtil.java:57)
at org.codehaus.enunciate.contract.jaxb.Accessor.<init>(Accessor.java:65)
at org.codehaus.enunciate.contract.jaxb.Element.<init>(Element.java:53)
at org.codehaus.enunciate.contract.jaxb.TypeDefinition.<init>(TypeDefinition.java:141)
at org.codehaus.enunciate.apt.GenericTypeDefinition.<init>(GenericTypeDefinition.java:33)
at org.codehaus.enunciate.apt.EnunciateFreemarkerModel.isSimpleType(EnunciateFreemarkerModel.java:1134)
at org.codehaus.enunciate.apt.EnunciateFreemarkerModel.createTypeDefinition(EnunciateFreemarkerModel.java:1059)
at org.codehaus.enunciate.apt.EnunciateFreemarkerModel.addReferencedTypeDefinitions(EnunciateFreemarkerModel.java:637)
at org.codehaus.enunciate.apt.EnunciateFreemarkerModel.add(EnunciateFreemarkerModel.java:612)
at org.codehaus.enunciate.apt.EnunciateAnnotationProcessor.getRootModel(EnunciateAnnotationProcessor.java:205)
at org.codehaus.enunciate.apt.EnunciateAnnotationProcessor.process(EnunciateAnnotationProcessor.java:102)
at com.sun.mirror.apt.AnnotationProcessors$CompositeAnnotationProcessor.process(AnnotationProcessors.java:60)
at com.sun.tools.apt.comp.Apt.main(Apt.java:454)
at com.sun.tools.apt.main.JavaCompiler.compile(JavaCompiler.java:258)
at com.sun.tools.apt.main.Main.compile(Main.java:1102)
at com.sun.tools.apt.main.Main.compile(Main.java:964)
at com.sun.tools.apt.Main.processing(Main.java:95)
at com.sun.tools.apt.Main.process(Main.java:85)
at com.sun.tools.apt.Main.process(Main.java:67)
at org.codehaus.enunciate.main.Enunciate.invokeApt(Enunciate.java:776)
at org.codehaus.enunciate.main.Enunciate.doGenerate(Enunciate.java:365)
at org.codehaus.enunciate.ConfigMojo$MavenSpecificEnunciate.doGenerate(ConfigMojo.java:634)
at org.codehaus.enunciate.main.Enunciate$Stepper.step(Enunciate.java:1706)
at org.codehaus.enunciate.main.Enunciate$Stepper.stepTo(Enunciate.java:1738)
at org.codehaus.enunciate.DocsMojo.execute(DocsMojo.java:95)
... 21 more

Source of the type adapter https://bitbucket.org/sdorra/scm-manager/src/tip/scm-core/src/main/java/sonia/scm/xml/XmlSetStringAdapter.java