the current syntax doesn't work properly in Rails 5, the resulting query
looks like:
HAVING "events"."project_id" IN (0)

instead of:
HAVING "events"."project_id" IN (SELECT "projects"."id" FROM...

Also we should not use ActiveRecord internal methods. In this case we
can filter projects in WHERE clause instead of doing this in HAVING
clause. Usage of WHERE should be also more efficient because grouping
is then done on much smaller subset of records.