public static <E, F> GroupExpression<E, Set<F>> set(GroupExpression<E, F> groupExpression) {
        return new MixinGroupExpression<E, F, Set<F>>(groupExpression, GSet.createLinked(groupExpression));
    }
Create a new aggregating set expression using a backing LinkedHashSet

@param groupExpression values for this expression will be accumulated into a set
@param <E>
@param <F>
@return wrapper expression
querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java