Not able to edit pages with attachment anymore

Reproduction steps:

• On a fresh XWiki 15.10.8
• Install change request 1.13.2
• Deny edit rights for users
• Register / login with a new user
• Go to sandbox and click edit button

Expected result:

• The editor is properly loaded with attachments

Obtained result:

• a stack trace immediately appears

Note that apparently the bug doesn't reproduce on XWiki 16.3 for some reason. But in any case there's some bulletproofing to do on Change request side.

— Original description —

After Updating XWiki to 15.10.8 and CRAPP to 1.13.2 users can not edit pages anymore, if the pages contains an attachment.

These users have only these permissions:

• Read
• Change Request
  (Users with normal Write Permissions to the pages are not affected)

 If the users clicks on "edit" a stacktrace is displayed

Caused by: java.lang.NullPointerException: Cannot invoke "com.xpn.xwiki.doc.XWikiAttachmentContent.setContentDirty(boolean)" because the return value of "com.xpn.xwiki.doc.XWikiAttachment.getAttachment_content()" is null 

I will attach the full stacktrace.

Possible that the issues occours because of the change in XWIKI-21270