Add nullable annotation

It looks like from the stack trace that there is an NPE during the setApps() call. So adding nullable and null checking
to make sure mApps is not null.

bug: 296920692
test: presubmit
flag: n/a
Change-Id: If402c0b68db159f7a698e8e2e139d9bd5041b1c1
2 files changed