Unnecessary Database Call?

[Sepero]

In the middleware, a database call is made to find goals that match the currently running experiments.
experiments = request.session.get(ACTIVE_EXPERIMENTS,[])
for goal in Goal.objects.filter(experiment__id__in=experiments,experiment__url_pattern__isnull=False):

If there are no experiments, is the database still accessed, or does the filter recognize this and return an empty set without accessing the database?