javax.servlet.ServletException: java.lang.RuntimeException: Failed to serialize org.jenkinsci.plugins.cloudstats.CloudStatistics#active for class org.jenkinsci.plugins.cloudstats.CloudStatistics
        at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:796)
        at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
        at org.kohsuke.stapler.MetaClass$4.doDispatch(MetaClass.java:211)
        at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
        at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
        at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
        at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249)
        at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
        at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
        at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
        at org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)
        at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
        at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:686)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1494)
        at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:123)
        at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:114)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
        at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
        at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
        at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
        at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:168)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
        at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
        at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
        at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1474)
        at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:499)
        at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
        at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533)
        at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
        at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
        at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428)
        at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
        at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
        at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
        at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
        at org.eclipse.jetty.server.Server.handle(Server.java:370)
        at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
        at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:960)
        at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1021)
        at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:957)
        at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)
        at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
        at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668)
        at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
        at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.RuntimeException: Failed to serialize org.jenkinsci.plugins.cloudstats.CloudStatistics#active for class org.jenkinsci.plugins.cloudstats.CloudStatistics
        at hudson.util.RobustReflectionConverter$2.writeField(RobustReflectionConverter.java:214)
        at hudson.util.RobustReflectionConverter$2.visit(RobustReflectionConverter.java:182)
        at com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider.visitSerializableFields(PureJavaReflectionProvider.java:138)
        at hudson.util.RobustReflectionConverter.doMarshal(RobustReflectionConverter.java:167)
        at hudson.util.RobustReflectionConverter.marshal(RobustReflectionConverter.java:108)
        at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:69)
        at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:58)
        at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:43)
        at com.thoughtworks.xstream.core.TreeMarshaller.start(TreeMarshaller.java:82)
        at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.marshal(AbstractTreeMarshallingStrategy.java:37)
        at com.thoughtworks.xstream.XStream.marshal(XStream.java:1026)
        at com.thoughtworks.xstream.XStream.marshal(XStream.java:1015)
        at com.thoughtworks.xstream.XStream.toXML(XStream.java:988)
        at hudson.XmlFile.write(XmlFile.java:178)
        at org.jenkinsci.plugins.cloudstats.CloudStatistics.save(CloudStatistics.java:219)
        at org.jenkinsci.plugins.cloudstats.CloudStatistics.persist(CloudStatistics.java:224)
        at org.jenkinsci.plugins.cloudstats.CloudStatistics.access$100(CloudStatistics.java:68)
        at org.jenkinsci.plugins.cloudstats.CloudStatistics$ProvisioningListener.onStarted(CloudStatistics.java:307)
        at com.redhat.jenkins.nodesharingfrontend.SharedNode.init(SharedNode.java:72)
        at com.redhat.jenkins.nodesharingfrontend.SharedNodeCloud.createNode(SharedNodeCloud.java:280)
        at com.redhat.jenkins.nodesharingfrontend.Api.doUtilizeNode(Api.java:188)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:298)
        at org.kohsuke.stapler.interceptor.RequirePOST$Processor.invoke(RequirePOST.java:46)
        at org.kohsuke.stapler.Function$InterceptedFunction.invoke(Function.java:399)
        at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:161)
        at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
        at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:121)
        at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
        at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
        ... 52 more
Caused by: java.util.ConcurrentModificationException
        at java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:711)
        at java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:734)
        at com.thoughtworks.xstream.converters.collections.CollectionConverter.marshal(CollectionConverter.java:73)
        at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:69)
        at com.thoughtworks.xstream.core.TreeMarshaller.convertAnother(TreeMarshaller.java:58)
        at com.thoughtworks.xstream.core.AbstractReferenceMarshaller$1.convertAnother(AbstractReferenceMarshaller.java:84)
        at hudson.util.RobustReflectionConverter.marshallField(RobustReflectionConverter.java:223)
        at hudson.util.RobustReflectionConverter$2.writeField(RobustReflectionConverter.java:210)
        ... 84 more