protected function departments()
    {
        //Avoid using FOL because is a transversal department
        if ( ! $this->filtersAppliedToDepartments()) return $this->validateCollection(Department::whereNotIn('department_id', [3])->get());
        if ( ! is_numeric($this->filters[1]) )  throw new \InvalidArgumentException();
        return collect([Department::findOrFail(intval($this->filters[1]))]);
    }