gitlab 7.5.1 crashes attempting to restore wikis

gitlab:backup:restore crashed when trying to restore any active wiki, even if the wiki already existed previously. This deletes the wiki, losing all the contents.

I was testing the new version 7.5.1, and did a backup restore cycle to make sure it worked. However, while issue #815 (closed) was fixed, the restore still crashed, given a valid wiki.

Partial list of backup:

Dumping repositories ...
 * raphael.schmidt/hipchat-perl ... [DONE]
 * raphael.schmidt/hipchat-perl.wiki ...  [SKIPPED]
 * gabriel.provencher/coffee_redmine_theme ... [DONE]
 * gabriel.provencher/coffee_redmine_theme.wiki ...  [SKIPPED]
 * intello/tccs ... [DONE]
 * intello/tccs.wiki ...  [SKIPPED]
 * impact/hub ... [DONE]
 * impact/hub.wiki ...  [DONE]

then the restore:

Restoring repositories ...
raphael.schmidt/hipchat-perl ... [DONE]
gabriel.provencher/coffee_redmine_theme ... [DONE]
intello/tccs ... [DONE]
impact/hub ... [DONE]
 * impact/hub.wiki ...  [FAILED]
Restore failed

This is probably connected to comment https://gitlab.com/gitlab-org/gitlab-ce/issues/832#note_620477, but in my case the wiki is not empty.

BTW, this worked fine before 7.5.1