Unable to get the Link between the two CAD files

Hi,

I am working on the one utility where I am trying the get the link between the two CAD objects I know they are associated with the Memberlink and for that I am using EMPMemberlink class but when I run the code it returns me the null. can any one tell me actual code through which I can get the Memberlink

where epm = SCISSORS.ASM and doc = BASE_SCISSOR.PRT

public static EPMMemberLink getMemberLink(EPMDocument epm, EPMDocument doc) throws WTException

                    {

                              EPMMemberLink link = null;

                              QueryResult queryLink = PersistenceHelper.manager.find(EPMMemberLink.class, epm, EPMMemberLink.ALL_ROLES, doc);

                              while(queryLink.hasMoreElements())

                              {

                                        link = (EPMMemberLink)queryLink.nextElement();

                              }

                              return link;

                    }