When I tried to use multipart-put to test concurrent multipart uploads, I expected it to create multipart parts completely, just like warp-multipart.
However, the multipart-put benchmark always sends an empty CompleteMultipartUploadRequest XML to the storage, which leads to server errors:

<CompleteMultipartUpload xmlns=\"http://s3.amazonaws.com/doc/2006-03-01/\"></CompleteMultipartUpload>

For example, I receive an error when testing with MinIO:

<Error><Code>InvalidRequest</Code><Message>You must specify at least one part</Message>...

The issue occurs because multipart-put does not include part information in completeMultipartInfo, whereas the multipart benchmark does.

Steps to reproduce:

1. Deploy default Minio (e.g. with Docker)
2. run benchmark as follows and you will see many <warp: complete multipart upload> errors:

./warp multipart-put --host 127.0.0.1:9000 \
                      --access-key=minioadmin \
                      --secret-key=minioadmin \
                          --parts=10 --part.size=5MiB --part.concurrent=5 --concurrent=5 \
                          --duration=5s \
                          --bucket=testbucket