After launching EC2 build agent, on Jenkins server side, under logs/slaves/<agent name>/slave.log, there is an error with stack as below. I noticed this because I want to modify the new agent idle time to debug, and it returns jenkins error (angry butlers) 

Here is the stack:

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Communication Protocol: Standard in/out
This is a Unix agent
ERROR: Unexpected error in launching an agent. This is probably a bug in Jenkins
Also:   hudson.remoting.Channel$CallSiteStackTrace: Remote call to EC2 (ec2-xxxxxx) - Build Agent (i-xxxxxxxxxxxxx)
at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1787)
at hudson.remoting.UserRequest$ExceptionResponse.retrieve(UserRequest.java:356)
at hudson.remoting.Channel.call(Channel.java:1003)
at hudson.FilePath.act(FilePath.java:1317)
at org.jenkinsci.plugins.envinject.EnvInjectComputerListener.onOnline(EnvInjectComputerListener.java:144)
at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:751)
at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:441)
at hudson.plugins.ec2.ssh.EC2UnixLauncher.launchScript(EC2UnixLauncher.java:284)
at hudson.plugins.ec2.EC2ComputerLauncher.launch(EC2ComputerLauncher.java:48)
at hudson.slaves.SlaveComputer.lambda$_connect$0(SlaveComputer.java:297)
at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
at jenkins.security.ImpersonatingExecutorService$2.call(ImpersonatingExecutorService.java:80)
java.lang.reflect.InaccessibleObjectException: Unable to make private native java.lang.reflect.Field[] java.lang.Class.getDeclaredFields0(boolean) accessible: module java.base does not "opens java.lang" to unnamed module @18f91981
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354)
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)
at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
at org.jenkinsci.plugins.envinject.service.EnvInjectMasterEnvVarsSetter.getModifiers(EnvInjectMasterEnvVarsSetter.java:29)
at org.jenkinsci.plugins.envinject.service.EnvInjectMasterEnvVarsSetter.call(EnvInjectMasterEnvVarsSetter.java:55)
at org.jenkinsci.plugins.envinject.service.EnvInjectMasterEnvVarsSetter.call(EnvInjectMasterEnvVarsSetter.java:19)
at hudson.remoting.UserRequest.perform(UserRequest.java:211)
at hudson.remoting.UserRequest.perform(UserRequest.java:54)
at hudson.remoting.Request$2.run(Request.java:377)
at hudson.remoting.InterceptingExecutorService.lambda$wrap$0(InterceptingExecutorService.java:78)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)
Agent successfully connected and online