java.lang.RuntimeException: Failed to serialize hudson.model.Project#buildWrappers for class hudson.model.FreeStyleProject
	at hudson.util.RobustReflectionConverter$2.writeField(RobustReflectionConverter.java:167)
	at hudson.util.RobustReflectionConverter$2.visit(RobustReflectionConverter.java:135)
	at com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider.visitSerializableFields(PureJavaReflectionProvider.java:130)
	at hudson.util.RobustReflectionConverter.doMarshal(RobustReflectionConverter.java:120)
	at hudson.util.RobustReflectionConverter.marshal(RobustReflectionConverter.java:94)
	at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:68)
	at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:78)
	at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:63)
	at com.thoughtworks.xstream.core.TreeMarshaller.start(TreeMarshaller.java:98)
	at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.marshal(AbstractTreeMarshallingStrategy.java:38)
	at com.thoughtworks.xstream.XStream.marshal(XStream.java:840)
	at com.thoughtworks.xstream.XStream.marshal(XStream.java:829)
	at com.thoughtworks.xstream.XStream.toXML(XStream.java:804)
	at hudson.XmlFile.write(XmlFile.java:173)
	at hudson.model.AbstractItem.save(AbstractItem.java:417)
	at hudson.model.Job.save(Job.java:150)
	at hudson.util.PersistedList.onModified(PersistedList.java:152)
	at hudson.util.PersistedList.replaceBy(PersistedList.java:79)
	at hudson.util.DescribableList.rebuild(DescribableList.java:165)
	at hudson.model.Project.submit(Project.java:196)
	at hudson.model.Job.doConfigSubmit(Job.java:966)
	at hudson.model.AbstractProject.doConfigSubmit(AbstractProject.java:643)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:282)
	at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:149)
	at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:88)
	at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:104)
	at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
	at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:561)
	at org.kohsuke.stapler.Stapler.invoke(Stapler.java:646)
	at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:234)
	at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
	at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:561)
	at org.kohsuke.stapler.Stapler.invoke(Stapler.java:646)
	at org.kohsuke.stapler.Stapler.invoke(Stapler.java:477)
	at org.kohsuke.stapler.Stapler.service(Stapler.java:159)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:45)
	at winstone.ServletConfiguration.execute(ServletConfiguration.java:249)
	at winstone.RequestDispatcher.forward(RequestDispatcher.java:335)
	at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:378)
	at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:95)
	at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:87)
	at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
	at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
	at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47)
	at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
	at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
	at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
	at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
	at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
	at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
	at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
	at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
	at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
	at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
	at winstone.RequestDispatcher.forward(RequestDispatcher.java:333)
	at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:244)
	at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150)
	at java.lang.Thread.run(Thread.java:680)
Caused by: org.jruby.exceptions.RaiseException: (TypeError) cannot convert instance of class org.jruby.RubyObject to class ruby.RubyPlugin