Added annotations to the APIs

Added @Nullable and @NonNull to several APIs.

Test: Manual
Bug: 126701840
Bug: 126702171
Bug: 126702057
Bug: 126702564
Bug: 126703014
Bug: 126702900

Change-Id: Ib4d8b2b45b11ef5d70cd229f33b8c8f903e5e6ee