Fix comments typo, rename param, refine obtainMessage

1. fix typo of omit;
2. change param name from "value" to a meaningful "sync";
3. seems obtainMessage can be refined as one line;
Comparing with just adding if () statement, i think maybe add an AssertUtils#assert method which throws exception if expression fails to let it fails as fast as possible instead of hiding an actual problem. What do you guys say?