question: public void addToExistingVolumesIfAbsent ( Map < String , Integer > volumeWWNs ) { if ( _existingVolumes == null ) { _existingVolumes = new StringMap ( ) ; } for ( String wwn : volumeWWNs . keySet ( ) ) { String normalizedWWN = BlockObject . normalizeWWN ( wwn ) ; if ( ! _existingVolumes . containsKey ( normalizedWWN ) && ( _userAddedVolumes == null || ! _userAddedVolumes . containsKey ( normalizedWWN ) ) ) { String hluStr = ExportGroup . LUN_UNASSIGNED_STR ; Integer hlu = volumeWWNs . get ( normalizedWWN ) ; if ( hlu != null ) { hluStr = hlu . toString ( ) ; } _existingVolumes . put ( normalizedWWN , hluStr ) ; } } }
target:  This method will add to the existing volumes list only those members that don't already exist in either the existing or user-created volume list.