Mention notification request fails with 500 status code

[Rash419]

Describe the bug Mention notification request fails with 500 status code

To Reproduce Steps to reproduce the behavior:

1. Create a account that have ' '(space) in the Display Name for example: Alison Burger
2. Share Document between two users
3. mention @Alison Burger in the document
4. Check console

Stacktrace:

/We</<
[xhr.js:195:12](webpack:///richdocuments/node_modules/axios/lib/adapters/xhr.js)
715/We<
[xhr.js:15:9](webpack:///richdocuments/node_modules/axios/lib/adapters/xhr.js)
vt
[dispatchRequest.js:51:17](webpack:///richdocuments/node_modules/axios/lib/core/dispatchRequest.js)
_request
[Axios.js:173:32](webpack:///richdocuments/node_modules/axios/lib/core/Axios.js)
request
[Axios.js:40:24](webpack:///richdocuments/node_modules/axios/lib/core/Axios.js)
715/</t/<
[Axios.js:212:18](webpack:///richdocuments/node_modules/axios/lib/core/Axios.js)
715/a/<
[bind.js:5:14](webpack:///richdocuments/node_modules/axios/lib/helpers/bind.js)
uiMention
[uiMention.js:38:16](webpack:///richdocuments/src/mixins/uiMention.js)
postMessageHandler
[Office.vue:433](webpack:///richdocuments/src/view/Office.vue)
e.prototype.handlePostMessage/<
[postMessage.tsx:74:19](webpack:///richdocuments/src/services/postMessage.tsx)
e.prototype.handlePostMessage
[postMessage.tsx:68:33](webpack:///richdocuments/src/services/postMessage.tsx)
e/<
[postMessage.tsx:12:18](webpack:///richdocuments/src/services/postMessage.tsx)
(Async: EventListener.handleEvent) e
[postMessage.tsx:11:15](webpack:///richdocuments/src/services/postMessage.tsx)

Request:

{"mention":"Alexandra Martini"}

Response:

<?xml version="1.0"?>
<ocs>
 <meta>
  <status>failure</status>
  <statuscode>500</statuscode>
  <message>Internal Server Error
</message>
 </meta>
 <data/>
</ocs>

Expected behavior No errors and user should be notified

Nextcloud log entry NoUserException Backends provided no user object

Server details

Nextcloud version: 30.0.1

Version of the richdocuments app: 8.5.2

Version of Collabora Online - latest master

[pedropintosilva]

cc @elzody