Correct nullability and final constraints on new APIs.

Per API review, correct nullability and final constraints on new Telecom
APIs.

Test: Build API.
Fixes: 126700293
Fixes: 126699447
Fixes: 126700465
Fixes: 126702895
Fixes: 126702527
Change-Id: Ic19664b156410e79a307b2af0d5672dc19f93c59
Merged-In: Icec15403493de596194a61b27bb3e1031fdc1099