1026 allow solr lookup by slug field

Do we actually need both cases? `document[:pid] || document['pid']` Is so, maybe we should be using `HashWithIndifferentAccess`, just so similar bits of code elsewhere don't get tripped up?

Is the `rescue` to handle the case where `document == nil`? Would something like this do what we want?
```ruby
pid = document && (document[:pid] || document['pid']) || params[:id]
```
  
```