Allow default value for header lookup.
Allow default value for header lookup.

K2InformaticsGmbH/elli,odo/elli,tsloughter/elli,knutin/elli,odo/elli,K2InformaticsGmbH/elli,elli-lib/elli,knutin/elli,tsloughter/elli,elli-lib/elli