code: public <T> ListenableFuture<Result<T>> queryAsync(final Class<T> entityClass,
        final Statement statement) {
      Mapper<T> mapper = mapper(entityClass);
      Session session = mapper.getManager().getSession();
      ResultSetFuture rs = session.executeAsync(statement);
      return Futures.transformAsync(rs, rs1 -> Futures.immediateFuture(mapper.map(rs1)));
    }
docs: Execute a query and map result to entityClass.
  
  @param entityClass Entity class.
  @param statement Statement to execute.
  @return A listenable future holding the result.