tree a1a89d2bfdd7c9eb67527bd207df81a7e3c1120a
parent 4b20e0c312d7a6f5f0a65e8bada74eeb52c15bc0
author Tony Wickham <twickham@google.com> 1486657732 -0800
committer Tony Wickham <twickham@google.com> 1486665006 -0800

Create a singleton HashMap instead of using Collections.singleton()

The Set returned by Collections.singleton() doesn't support all
operations, causing crashes in certain situations (namely, whenever
a notification is updated rather than added or removed).

Change-Id: Ie104b7f99c4a32db5f1f7e43ec3775d34dc26ce1