question: public void putMap ( Map < String , List < String > > m ) { for ( String key : m . keySet ( ) ) { SortedSet < String > vals = get ( key ) ; if ( vals == null ) { vals = new TreeSet < String > ( ) ; put ( key , vals ) ; } vals . addAll ( m . get ( key ) ) ; } }
target:  Convenience method to merge a Map<String, List<String>>.