Updating EPMDocument attributes through a promotion request

Hi .

I'd like to update a couple of attribute belonging to a EPMDocument associated with a PromotionNotice object in a promotion request workflow.

I've chosen the following method to accomplish this:

LWCNormalizedObject obj = new LWCNormalizedObject(my_persistable,null,Locale.US,new UpdateOperationIdentifier());

obj.load("attributeA","attribtueB");

obj.set("attributeA",Boolean.TRUE);

obj.set("attribtueB","Hello World");

obj.apply();

PersistenceHelper.manager.modify(my_persistable);

When i make a new promotion request from the windchill UI the attributes are'nt updated at all. Looking through the logfile led me to this error.

(wt.vc.wip.wipResource/47) wt.vc.wip.WorkInProgressException: The object is not checked out and cannot be modified.

I've concluded that it's (PersistenceHelper.manager.modify(my_persistable);) that trows the error.

my_persistable is set by iterating through the query result returned from a call to MaturityHelper.service.getPromotionTarget(PromotionNotice).

What am i doing wrong here ?