triAGENS/guacamole — pull request #20 by railsbros-dirk (2013-10-20 15:00:32+00:00)
Title: Collection.by_key should return DocumentNotFound for nil

Currently this results in a bad request when talking to ArangoDB:

```ruby
UsersCollection.by_key(123)
# #
>> UsersCollection.by_key(nil)
# #
```

For `nil` there should be a `DocumentNotFoundException` too.