code: public static Bson lookup(final String from, final List<? extends Bson> pipeline, final String as) {
          return lookup(from, null, pipeline, as);
      }
docs: Creates a $lookup pipeline stage, joining the current collection with the one specified in from using the given pipeline
  
  @param from          the name of the collection in the same database to perform the join with.
  @param pipeline      the pipeline to run on the joined collection.
  @param as            the name of the new array field to add to the input documents.
  @return the $lookup pipeline stage
  @mongodb.driver.manual reference/operator/aggregation/lookup/ $lookup
  @mongodb.server.release 3.6
  @since 3.7