@Override
            protected TreeMultimap<K, V> transform(Multimap<K, Group> groups) {
                TreeMultimap<K, V> results = (TreeMultimap) TreeMultimap.create();
                for (Map.Entry<K, Group> entry : groups.entries()) {
                    results.put(entry.getKey(), entry.getValue().getOne(lookup));
                }
                return results;
            }
Get the results as multi map

@param expression value expression
@param <V> Value type
@return new result transformer
querydsl-guava/src/main/java/com/querydsl/core/group/guava/GuavaGroupByBuilder.java