Fix request #5758 - Fatal error when trying to update an artifact

Change-Id: I7e0a197ed4f1604dfa8e0fec833d356833c0e0bc
Merge commit 'refs/changes/68/1568/1' of http://gerrit.tuleap.net/tuleap into HEAD

* http://gerrit.tuleap.net/tuleap:
  Fix request #5758 - Fatal error when trying to update an artifact

Change-Id: If32d2a3b3f7d8e4fc3c0a8b6b0c591a2b3ef59c5
This is Tuleap 6.8.99.1

Change-Id: I06cd9a762d736f5d409a461e1e9557ff0379fb06