Steps to reproduce :
- Create an instance with XWiki 8.4.5
- Specify that the attachment storage of this instance should be on the filesystem and not in the db with xwiki.store.attachment.hint=file
- Start the wiki
- Add an attachment with spaces in its name to the home page (for example : "a doc with spaces.txt")
- Upgrade the instance to 11.3 (either by replacing the WAR, or moving the DB and the perm dir). FS attachments is enabled by default, so no need to update the configuration.
- Start the wiki and go on the home page
- Observe that, when clicking on the attachment, the attachment can't be found by XWiki.