code: @NotNull
    public CompletableFuture<Meta> upload(@NotNull final Meta meta, @NotNull final StreamProvider streamProvider) {
      return enqueue(meta, streamProvider);
    }
docs: This method start uploading object to server.
  
  @param meta           Object metadata.
  @param streamProvider Stream provider.
  @return Return future with upload result. For same objects can return same future.