code: @NonNull
      @Override
      public ObservableTransformer<ParseSingleGroupOp, Card> getSingleGroupTransformer() {
          return new ObservableTransformer<ParseSingleGroupOp, Card>() {
              @Override
              public ObservableSource<Card> apply(Observable<ParseSingleGroupOp> upstream) {
                  return upstream.map(new Function<ParseSingleGroupOp, Card>() {
                      @Override
                      public Card apply(ParseSingleGroupOp parseSingleGroupOp) throws Exception {
                          return parseSingleGroup(parseSingleGroupOp.getArg1(), parseSingleGroupOp.getArg2());
                      }
                  });
              }
          };
      }
docs: {@inheritDoc}