public boolean add(K key,V item){
  Set<V> values=map.get(key);
  if (values == null) {
    values=(sorted ? new TreeSet<V>() : new HashSet<V>());
    map.put(key,values);
  }
  if (item == null)   return false;
  return values.add(item);
}

public boolean add ( K key , V item ) { Set < V > values = map . get ( key ) ; if ( values == null ) { values = ( sorted ? new TreeSet < V > ( ) : new HashSet < V > ( ) ) ; map . put ( key , values ) ; } if ( item == null ) return false ; return values . add ( item ) ; }
adds item to the set of values associated with the key ( null items are not added )
