public static <K, V, U> AbstractGroupExpression<Pair<K, V>, Map<K, U>> map(Expression<K> key,
                                                                               GroupExpression<V, U> value) {
        return map(new GOne<K>(key), value);
    }
Create a new aggregating map expression using a backing LinkedHashMap

@param key key for the map entries
@param value value for the map entries
@return wrapper expression
querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java