Error raise when changing a 'None' data to a new format:
"TypeError: 'NoneType' object is not iterable"
we also met that bug before in the previous patch [1]
This change is to handle the 'None' data and avoid
the error
[1] https://review.openstack.org/#/c/420420/
Change-Id: I649b4fc65ef7c19b8193b07f3bd59f00e6095f9f
Closes-bug: #1656363