Fix NPE

Treehugger didn't hit this with the original CL (ag/9721403) but I'm
hitting it locally & believe it is the root cause of attached bug.

Test: atest NotificationManagerTest (doesn't crash)
Bug: 144947853
Bug: 144958550
Change-Id: I3a03097b1e81b81a1847ef46422a052df726eb7d