One of my 400 Jenkins plugins is frequently throwing this error in my Jenkins log. But which plugin ??? 

rejecting javax.management.RuntimeErrorException according to standard blacklist; see https://jenkins.io/redirect/class-filter/
java.lang.SecurityException: Class rejected by the class filter: javax.management.RuntimeErrorException
at jenkins.security.ClassFilterImpl.notifyRejected(ClassFilterImpl.java:335)
at jenkins.security.ClassFilterImpl.isBlacklisted(ClassFilterImpl.java:323)
at hudson.remoting.ClassFilter$1.isBlacklisted(ClassFilter.java:125)
at hudson.remoting.ClassFilter.check(ClassFilter.java:64)
at hudson.remoting.MultiClassLoaderSerializer$Input.resolveClass(MultiClassLoaderSerializer.java:130)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1819)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1713)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1986)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1535)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:422)
at hudson.remoting.UserRequest.deserialize(UserRequest.java:291)
at hudson.remoting.UserRequest$ExceptionResponse.retrieve(UserRequest.java:349)
at hudson.remoting.Channel$2.adapt(Channel.java:992)
at hudson.remoting.Channel$2.adapt(Channel.java:988)
at hudson.remoting.FutureAdapter.get(FutureAdapter.java:59)
at net.bull.javamelody.RemoteCallHelper.collectDataByNodeName(RemoteCallHelper.java:201)
at net.bull.javamelody.RemoteCallHelper.collectJavaInformationsListByName(RemoteCallHelper.java:213)
at net.bull.javamelody.NodesCollector.collectWithoutErrorsNow(NodesCollector.java:159)
at net.bull.javamelody.NodesCollector.collectWithoutErrors(NodesCollector.java:147)
at net.bull.javamelody.NodesCollector$1.run(NodesCollector.java:91)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)