code: public void pipe(final BsonReader reader, final List<BsonElement> extraElements) {
          notNull("reader", reader);
          notNull("extraElements", extraElements);
          pipeDocument(reader, extraElements);
      }
docs: Reads a single document from the given BsonReader and writes it to this, appending the given extra elements to the document.
  
  @param reader the source of the document
  @param extraElements the extra elements to append to the document
  @since 3.6