Comment 3 for bug 1327473

Reviewed: https://review.openstack.org/98339
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=0bea84ac20fe498bd08f7212a0017196c8cb0812
Submitter: Jenkins
Branch: master

commit 0bea84ac20fe498bd08f7212a0017196c8cb0812
Author: ChangBo Guo(gcb) <email address hidden>
Date: Sat Jun 7 10:49:20 2014 +0800

    Removes the use of mutables as default args

    Passing mutable objects as default args is a known Python pitfall.
    We'd better avoid this. This commit changes mutable default args with
    None, then use 'arg = arg or {}', 'arg = arg or []'. For unit code which
    doesn't use the args , just set with None. This commit also adds hacking
    check.

    Closes-Bug: #1327473
    Change-Id: I5a8492bf8ffef8e000b13b6bdfaef1968b96f816