Workflow Java Node issues

I am developing a functionality to be used as a java node inside the workflow. I have followed the "javanodeexample.java" as an example to develop this.

But i am getting error specifically on the " catch (PersistenceException e1) {
      return false;
    } "

I have used the server.jar as the reference , there are no compilation errors except the below:-

"persistence exception must be subclass of throwable"

And also  i have imported the following

import com.aveksa.server.core.cr.ChangeRequest;
import com.aveksa.server.db.PersistenceException;
import com.aveksa.server.workflow.scripts.WorkflowContext;
import org.apache.log4j.Logger;

still the error is only in the

catch (PersistenceException e1) {
      return false;
    } "

Please let me know if i am missing anything