When a query has many joins nested, the construction of `params` is very slow. This is mainly because `params` is called twice in `Join`, once for `hasattr` test and and second times to extend the list. As the joins are nested, this has an `O(2*n!)` and so it can be very slow pretty quickly. Ref: https://discuss.tryton.org/t/performance-issue-computing-query-params/7223