Not getting _id when searching with Java API

Hello,

I have the following problem: I am searching an index using the Java API. Everything works fine, except I am not getting back the _id of the search hits. I tried to insert _id into the fields, I also tried an empty field (as I understand in this case _id should be returned by default). Neither works for me. What is the proper way to return the id of serach hits in Java?

Thanks!
Andrej