I guess we have two questions:
If you are filtering ANY OF and you pass an empty list, what do you expect to come back?
If you are filtering ALL OF and you pass an empty list, what do you expect to come back?

In the test case I give the example of filtering blog_id. We're trying to find blog posts from the list of blog_ids. If that list is empty, I would expect to find no posts in the results.

With that said, I could also see the case where we are filtering on tags and are given an empty list. In that case one might expect not to have the filter apply at all.

Either behaviour can easily be achieved with 

```ruby
with(:field, filter_tags) if filter_tags.present?
```

However, I think the blog_id behaviour is more "normal" than the tag behaviour.

Thoughts?