An empty query value that is a string should not return all documents.

Example
-----

Collection name is required.  There are zero objects in the database with an empty collection name.

#### Before
```ruby
pry(main)> Admin::Collection.where('name_tesim' => "").count
=> 12
```


#### After
```ruby
pry(main)> Admin::Collection.where('name_tesim' => "").count
=> 0
```

* Should I write tests for this?  Where should they go?
* Where should I put my change in HISTORY?  The latest release?