Null point check

When getting a notification by key, we must check if the
mNotificationsByKey map contains the record. not making a null pointer
check resulted in a runtime NullPointerException

Change-Id: I0026a2e74aabf4a6e622c50a1b915599abe4c174
Fix: 142398358
Test: manual test following the steps in the bug
1 file changed