protected  <V> Expression<V> getLookup(Expression<V> expression) {
        if (expression instanceof GroupExpression) {
            @SuppressWarnings("unchecked") // This is the underlying type
            GroupExpression<V, ?> groupExpression = (GroupExpression<V, ?>) expression;
            return groupExpression.getExpression();
        } else {
            return expression;
        }
    }
Get the results as a set

@param expression projection
@return new result transformer
querydsl-core/src/main/java/com/querydsl/core/group/GroupByBuilder.java