docs: @Override
      public <T> Flowable<Tx<T>> get(@Nonnull ResultSetMapper<? extends T> mapper) {
          Preconditions.checkNotNull(mapper, "mapper cannot be null");
          return Flowable.defer(() -> {
              AtomicReference<Connection> connection = new AtomicReference<Connection>();
              Flowable<T> o = Update.<T>createReturnGeneratedKeys( //
                      update.updateBuilder.connections //
                              .map(c -> Util.toTransactedConnection(connection, c)),
                      update.parameterGroupsToFlowable(), update.updateBuilder.sql, mapper, false);
              return o.materialize() //
                      .flatMap(n -> Tx.toTx(n, connection.get(), db)) //
                      .doOnNext(tx -> {
                          if (tx.isComplete()) {
                              ((TxImpl<T>) tx).connection().commit();
                          }
                      });
          });
      }