if this is a case i do not understand why you did not include this in your GC application
I-485 ask "Have you ever been arrested, cited, indicted, charged, convicted, fined, jailed for breaking or violating any law" rather than
"for any reason". If the OP did not think he violated any law and was just arrested for political dissence, he did not have to disclose
it if the question is taken literally.