Byte Buddy 1.9.x throws `java.lang.IllegalStateException: Cannot resolve type description for java.lang.String` errors. Is it a known issue? - mule

Question

I am seeing Cannot resolve type description errors when trying to load classes instrumented using Byte Buddy v1.9.11 within Mule 4 (JDK 1.8). Is there a known issue with Byte Buddy, or a particular combination of isolated classloader Mule 4 is using with Byte Buddy instrumented classes? Any suggestions are appreciated.
I am using Elastic Java APM agent to instrument Mule 4 with its over-complicated classloader isolation mechanism that seems to interfere with Byte Buddy v1.9.11 used by the APM agent.
java.lang.IllegalStateException: Cannot resolve type description for java.lang.String
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Resolution$Illegal.resolve(TypePool.java:159)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$TokenizedGenericType.toErasure(TypePool.java:6505)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$LazyTypeList.get(TypePool.java:6313)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$LazyTypeList.get(TypePool.java:6286)
at java.util.AbstractList$Itr.next(AbstractList.java:358)
at co.elastic.apm.agent.shaded.bytebuddy.matcher.ElementMatchers.takesArguments(ElementMatchers.java:1301)
at co.elastic.apm.agent.shaded.bytebuddy.dynamic.scaffold.inline.InliningImplementationMatcher.of(InliningImplementationMatcher.java:71)
at co.elastic.apm.agent.shaded.bytebuddy.dynamic.scaffold.inline.RedefinitionDynamicTypeBuilder.make(RedefinitionDynamicTypeBuilder.java:202)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$Transformation$Simple$Resolution.apply(AgentBuilder.java:10132)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:10551)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10514)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1500(AgentBuilder.java:10280)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10889)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10836)
at java.security.AccessController.doPrivileged(Native Method)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10437)
at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at org.mule.runtime.module.artifact.api.classloader.FineGrainedControlClassLoader.findLocalClass(FineGrainedControlClassLoader.java:171)
at org.mule.runtime.module.artifact.api.classloader.FineGrainedControlClassLoader.loadClass(FineGrainedControlClassLoader.java:88)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at co.elastic.apm.api.NoopTransaction.startSpan(NoopTransaction.java:132)
at co.elastic.apm.agent.utils.SpanUtils.startSpan(SpanUtils.java:34)
at co.elastic.apm.agent.internal.ApmMessageProcessorNotificationListener.onNotification(ApmMessageProcessorNotificationListener.java:27)
at co.elastic.apm.agent.internal.ApmMessageProcessorNotificationListener.onNotification(ApmMessageProcessorNotificationListener.java:10)
at org.mule.runtime.core.api.context.notification.ServerNotificationManager.lambda$fireNotification$0(ServerNotificationManager.java:193)
at org.mule.runtime.core.internal.context.notification.Sender.dispatch(Sender.java:28)
at org.mule.runtime.core.internal.context.notification.Policy.dispatchToSenders(Policy.java:146)
at org.mule.runtime.core.internal.context.notification.Policy.doDispatch(Policy.java:134)
at org.mule.runtime.core.internal.context.notification.Policy.dispatch(Policy.java:106)
at org.mule.runtime.core.api.context.notification.ServerNotificationManager.notifyListeners(ServerNotificationManager.java:211)
at org.mule.runtime.core.api.context.notification.ServerNotificationManager.fireNotification(ServerNotificationManager.java:193)
at org.mule.runtime.core.privileged.processor.chain.AbstractMessageProcessorChain.fireNotification(AbstractMessageProcessorChain.java:373)
at org.mule.runtime.core.privileged.processor.chain.AbstractMessageProcessorChain.lambda$preNotification$23(AbstractMessageProcessorChain.java:339)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:190)
at org.mule.runtime.core.privileged.processor.chain.AbstractMessageProcessorChain$1.onNext(AbstractMessageProcessorChain.java:292)
at org.mule.runtime.core.privileged.processor.chain.AbstractMessageProcessorChain$1.onNext(AbstractMessageProcessorChain.java:285)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onNext(FluxHide.java:127)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:204)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:204)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:204)
at reactor.core.publisher.FluxPublishOn$PublishOnSubscriber.runAsync(FluxPublishOn.java:398)
at reactor.core.publisher.FluxPublishOn$PublishOnSubscriber.run(FluxPublishOn.java:484)
at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84)
at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at org.mule.service.scheduler.internal.AbstractRunnableFutureDecorator.doRun(AbstractRunnableFutureDecorator.java:111)
at org.mule.service.scheduler.internal.RunnableFutureDecorator.run(RunnableFutureDecorator.java:54)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

Answer 1

I assume that the class file resolver used by the Elasticsearch agent is querying the class loader directly where this particular class loader is hiding the class files in question.
You can argue that this is an issue of the class loader hiding the class file or an issue of the elastic search agent not attempting other class loaders or reattempting the redefinition of the loaded class. I'd contact both entities as this can disturb different tooling.