Sometime, a 500 error happen after a merge

Most of the time during getComparisionForFile or getBranches

Steps to reproduce, with 2 users using simple mode:

• User 1 alters a document type and saves.
• Meanwhile, User 2 deletes the same document type.
• User 2 is presented with a conflict management popup.
• User 2 clicks on cancel.
  => An error 500 potentially appears
  => User 2 sees a push and a pull button, the push button should not appear as she is using the simple mode