code: public <T> ListenableFuture<Void> saveAsync(final T entity, final Mapper.Option... options) {
      Class entityClass = entity.getClass();
      Mapper mapper = mapper(entityClass);
      return mapper.saveAsync(entity, options);
    }
docs: Save an entity.
  
  @param entity Entity to save.
  @param options Options.
  @return An empty listenable future.