Fix NPE while reading leftover journals in BMS

Thisis the NPE bug we saw a while ago but it  has been coming up in test runs recently (b/). Let's fix the NPE for now and we can work on the underlying issue later.

Bug: 136730045
Test: atest DataChangedJournalTest
Change-Id: I7267f507be4c797491d86ebb8bc5e6c3c17652a3