How to get BaselinedPlan object

Hi,

I am trying to retrieve BaselinedPlan object using the OOTB api but when I try to get object it throws me class case exception. can any one tell me which API i can use to retrieve BaselinedPlan

code using:

PlanActivity pa = getPlanActivity(activityName, proj);  // get PlanActivity

  ObjectReference objRef = wt.fc.ObjectReference.newObjectReference(pa);

  com.ptc.projectmanagement.plan.baseline.BaselineHelper.service.getActiveBaseline(objRef);

Error Message : Caused by: java.lang.ClassCastException: com.ptc.projectmanagement.plan.baseline.BaselinedPlanActivity cannot be cast to com.ptc.projectmanagement.plan.baseline.BaselinedPlan