Getting NullPointerException when publishing publication structure using doPublish() method.

[JA_11399780]

I am trying below piece of code to publish publication structure using publishing rule. Can anyone guide me if anything wrong in what I am trying.

Publisher pub = new Publisher();
String objRef = ObjectReference.newObjectReference(pubStruct).toString();
if(!(WorkInProgressHelper.isCheckedOut(pubStruct))) {
    String actionString = "<wvsoptions>pubrulename=PS PDF **** Publishing Rule";
    boolean result = pub.doPublish(false, true, objRef,
          (ConfigSpec) null,
          (ConfigSpec) null, true, "Sample_Rep", "Sample_Rep_Desc",
          Publisher.EPM, actionString, 0);
}

I am getting the below error in methodserver.

wt.wvs.content.FileHelper - null java.lang.NullPointerException
	at wt.pom.PersistentObjectManager.expand(PersistentObjectManager.java:1409)
	at wt.fc.StandardPersistenceManager.expand(StandardPersistenceManager.java:3121)
	at wt.fc.StandardPersistenceManager.navigate(StandardPersistenceManager.java:497)
	at jdk.internal.reflect.GeneratedMethodAccessor357.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at wt.services.ServiceFactory$ServerInvocationHandler.invoke(ServiceFactory.java:399)
	at com.sun.proxy.$Proxy29.navigate(Unknown Source)
	at wt.content.StandardContentService.getContentsByRole(StandardContentService.java:2984)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at wt.services.ServiceFactory$ServerInvocationHandler.invoke(ServiceFactory.java:399)
	at com.sun.proxy.$Proxy67.getContentsByRole(Unknown Source)
	at com.ptc.wvs.server.util.FileHelper.getEdzFile(FileHelper.java:1242)
	at com.ptc.wvs.server.util.FileHelper.getEdzFile(FileHelper.java:1226)
	at com.ptc.wvs.server.publish.Publish.newPublishJobInstances(Publish.java:984)
	at com.ptc.wvs.server.publish.Publish.executePublish(Publish.java:1889)
	at com.ptc.wvs.server.publish.Publish.executePublish(Publish.java:1838)
	at com.ptc.wvs.server.publish.Publish.executePublish(Publish.java:705)
	at com.ptc.wvs.server.publish.Publish.doPublish(Publish.java:551)
	at com.ptc.wvs.server.publish.Publish.doPublish(Publish.java:360)
	at com.ptc.wvs.common.ui.Publisher.doClientPublish(Publisher.java:540)
	at com.ptc.wvs.common.ui.Publisher.doPublish(Publisher.java:494)

Kindly help.