Searching for WTPartDescribeLinks

I need to run a search for specific WTPartDescribeLinks from a checked out part.

The following line isn't working for me. I get an error stating the iteration must not be null. I believe the method has been deprecated.

//QueryResult qrLink = StructHelper.service.navigateDescribes(checkedOutPart, WTPartDescribeLink.class, false);

I have also tried

QueryResult qrLink = PersistenceHelper.manager.navigate(checkedOutPart,   WTPartDescribeLink.ROLE_AOBJECT_REF, WTPartDescribeLink.class, false);

But I am getting a Null Pointer Exception

Is there another way of running a search for these describe links or am I doing something wrong?

Any thoughts would be very much appreciated. Thanks

Regards,

Ryan