how to query small string customized attribute?

Hi Friends,

I created a customized attribute, type small string named "siglaSistema" but the query by this attribute broken

Here is the code:

WorkItemQueryModel model= WorkItemQueryModel.ROOT;
IItemQuery query= IItemQuery.FACTORY.newInstance(model);
IPredicate predicate = model.workItemType()._eq("FRM");
predicate = predicate._and(model.projectArea()._eq(projectArea));
predicate = predicate._and(model.stringExtensions().key()._eq("frm_classe_req_mudancas"))._and(model.stringExtensions().value()._eq("frm_classe_req_mudancas.literal.l6"));
predicate = predicate._and(model.stringExtensions().key()._eq("siglaSistema"))._and(model.stringExtensions().value()._eq((siglaSistema)));
predicate = predicate._and(model.internalState()._eq(wiDto.getAttributeValue()));

Am I doing somethng wrong?

Thank you for any help

Regards!