docs: private String initMultipartUpload(String bucketName, String objectName, Map<String, String> headerMap)
      throws InvalidBucketNameException, NoSuchAlgorithmException, InsufficientDataException, IOException,
             InvalidKeyException, NoResponseException, XmlPullParserException, ErrorResponseException,
             InternalException {
      // set content type if not set already
      if (headerMap.get("Content-Type") == null) {
        headerMap.put("Content-Type", "application/octet-stream");
      }
  
      Map<String,String> queryParamMap = new HashMap<>();
      queryParamMap.put("uploads", "");
  
      HttpResponse response = executePost(bucketName, objectName, headerMap, queryParamMap, "");
  
      InitiateMultipartUploadResult result = new InitiateMultipartUploadResult();
      result.parseXml(response.body().charStream());
      response.body().close();
      return result.uploadId();
    }