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;

}