Check whether the bands and channels are null

We need to first check whether bands and channels are null before
doing anything else on them.

Cherry-picked cleanly from:
https://android-review.googlesource.com/#/c/422286/

Test: Telephony sanity tests
Bug: 30954762

Merged-in: Idaa3ebeabe37248d9de05f8397fecc4dc9938d66
Change-Id: Idaa3ebeabe37248d9de05f8397fecc4dc9938d66
(cherry picked from commit c771233f)