[Transverse] Milestone missing in folder campaign deletion process

Affected version : 5.1 & 7.0.0

Steps to reproduce

Have a milestone associates to a project and so, at campaign and objects (folder, campaign, iteration...)
Have a folder in Campaign workspace of this project, and severals campaign into.
Try to delete this folder

observed behavior

Folder can't delete

Expeted result

Folder can be delete