code: public Consumer<AppendGroupsOp> asAppendGroupsConsumer() {
          return new Consumer<AppendGroupsOp>() {
              @Override
              public void accept(AppendGroupsOp op) throws Exception {
                  appendBatchWith(op.getArg1());
              }
          };
      }
docs: Make engine as a consumer to accept data to append at the end of list
  @return
  @since 3.0.0