[MAC rand] Avoid null Object of mac address

Bug: 140309663
Test: unit tests

Merged-In: I914a2678e62f1e2ef6dc1b358a76a306b9cc0cc4
Change-Id: Ibf281c5e25c21c17652d718c346c8b560aedcc72
(cherry picked from commit I914a2678e62f1e2ef6dc1b358a76a306b9cc0cc4)
2 files changed