We are using Jenkins version 2.73.2 and connected all the Jenkins slaves using Jenkins swarm client version 3.6. We are getting the below error while running a pipeline.

java.lang.NoClassDefFoundError: Could not initialize class hudson.util.Secret
    at sun.misc.Unsafe.ensureClassInitialized(Native Method)
    at sun.reflect.UnsafeFieldAccessorFactory.newFieldAccessor(UnsafeFieldAccessorFactory.java:43)
    at sun.reflect.ReflectionFactory.newFieldAccessor(ReflectionFactory.java:142)
    at java.lang.reflect.Field.acquireFieldAccessor(Field.java:1088)
    at java.lang.reflect.Field.getFieldAccessor(Field.java:1069)
    at java.lang.reflect.Field.getLong(Field.java:611)
    at java.io.ObjectStreamClass.getDeclaredSUID(ObjectStreamClass.java:1707)
    at java.io.ObjectStreamClass.access$700(ObjectStreamClass.java:72)
    at java.io.ObjectStreamClass$2.run(ObjectStreamClass.java:484)
    at java.io.ObjectStreamClass$2.run(ObjectStreamClass.java:472)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:472)
    at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:369)
    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:598)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1630)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1781)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2018)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1942)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1808)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2018)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1942)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1808)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)
    at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1714)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2018)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1942)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1808)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:373)
    at hudson.remoting.UserRequest.deserialize(UserRequest.java:275)
    at hudson.remoting.UserRequest.perform(UserRequest.java:186)
    at hudson.remoting.UserRequest.perform(UserRequest.java:54)
    at hudson.remoting.Request$2.run(Request.java:360)
    at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:68)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at hudson.remoting.Engine$1$1.run(Engine.java:98)
    at java.lang.Thread.run(Thread.java:745)
    at ......remote call to JNLP4-connect connection from slave1/192.168.1.25:44581(Native Method)
    at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1654)
    at hudson.remoting.UserResponse.retrieve(UserRequest.java:311)
    at hudson.remoting.Channel.call(Channel.java:905)
Caused: java.io.IOException: Remote call on JNLP4-connect connection from slave1/192.168.1.25:44581 failed
    at hudson.remoting.Channel.call(Channel.java:913)
    at hudson.remoting.RemoteInvocationHandler.invoke(RemoteInvocationHandler.java:257)
Caused: hudson.remoting.RemotingSystemException
    at hudson.remoting.RemoteInvocationHandler.invoke(RemoteInvocationHandler.java:273)
    at com.sun.proxy.$Proxy115.addCredentials(Unknown Source)
    at org.jenkinsci.plugins.gitclient.RemoteGitImpl.addCredentials(RemoteGitImpl.java:200)
    at hudson.plugins.git.GitSCM.createClient(GitSCM.java:771)
    at hudson.plugins.git.GitSCM.createClient(GitSCM.java:747)
    at hudson.plugins.git.GitSCM.checkout(GitSCM.java:1109)
    at org.jenkinsci.plugins.workflow.steps.scm.SCMStep.checkout(SCMStep.java:113)
    at org.jenkinsci.plugins.workflow.steps.scm.SCMStep$StepExecutionImpl.run(SCMStep.java:85)
    at org.jenkinsci.plugins.workflow.steps.scm.SCMStep$StepExecutionImpl.run(SCMStep.java:75)
    at org.jenkinsci.plugins.workflow.steps.AbstractSynchronousNonBlockingStepExecution$1$1.call(AbstractSynchronousNonBlockingStepExecution.java:47)
    at hudson.security.ACL.impersonate(ACL.java:260)
    at org.jenkinsci.plugins.workflow.steps.AbstractSynchronousNonBlockingStepExecution$1.run(AbstractSynchronousNonBlockingStepExecution.java:44)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    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:748)
Finished: FAILURE