docs: private String getCommitBody(List<BoxFileUploadSessionPart> parts, Map<String, String> attributes) {
          JsonObject jsonObject = new JsonObject();
  
          JsonArray array = new JsonArray();
          for (BoxFileUploadSessionPart part: parts) {
              JsonObject partObj = new JsonObject();
              partObj.add("part_id", part.getPartId());
              partObj.add("offset", part.getOffset());
              partObj.add("size", part.getSize());
  
              array.add(partObj);
          }
          jsonObject.add("parts", array);
  
          if (attributes != null) {
              JsonObject attrObj = new JsonObject();
              for (String key: attributes.keySet()) {
                  attrObj.add(key, attributes.get(key));
              }
              jsonObject.add("attributes", attrObj);
          }
  
          return jsonObject.toString();
      }