Using <ri:attachment> when updating page using API with /n will cause error

Issue Summary

A partner has reported an issue with <ri:attachment> when updating a page through the API ( /rest/api/content/<id>).

• When opening and closing the <ri:attachment>  tag in the same line, there are not issues and it works as expected.
• When opening <ri:attachment> in one line and closing it in a different line, it throws StorageUnmarshalXhtmlException

Steps to Reproduce

1. Using API to update confluence page
   example:

   { "type": "page", "version": \\{ "number": 3 },
   "title": "Attachments",
   "status": "historical",
   "body": {
   "storage":{ "representation": "storage", "value": "<ac:image ac:align=\"center\" ac:layout=\"center\" ac:original-height=\"600\" ac:original-width=\"1200\">\n <ri:attachment ri:filename=\"cat.png\" ri:version-at-save=\"1\">\n </ri:attachment>\n</ac:image>\n<p />" }
   }
   

Expected Results

Update success

Actual Results

HTTP 500 error
 

Workaround