Minor - P4 See: http://api.mongodb.org/java/3.0/com/mongodb/client/MongoCollection.html
<TResult> DistinctIterable<TResult> distinct(String fieldName, Class<TResult> resultClass)
Per the CRUD spec, this method should have a required filter parameter as its second argument:
distinct(fieldName: string, filter: Document, options: DistinctOptions): Iterable<any>;