Hi Davide,

I have almost done with the code. Need few more helps from you:

1. since MongoDb Driver distinct query returns List of objects , how can I convert it into ClosableIterator<Tuple> . I see MapTupleSnapshot and MongoDBTupleSnapshot but not sure which one to use!!! Or should I just use CollectionHelper

2. Once I am done with step 1, how should I create PR??
I have forked the repo already.

Thanks