code: public final <R> Iterable<R> mapReduce(String name, final MapReduceResultHandler<R> conv) {
          return this.mapReduce(name, null, null, null, conv);
      }
docs: runs a map-reduce-job on the collection. same as {@link #mapReduce(String, DBObject, DBObject, Map, MapReduceResultHandler)
  mapReduce(name, null, null, null, conv)}
  
  @param <R>  the type of the result class
  @param name the name of the map-reduce functions
  @param conv the converter to convert the result
  @return an {@link Iterable} with the result entries