no problem; nothing to worry about
Jocular, humorous phrase playing on 問題なし (no problem) by replacing なし with the English word 'nothing' written in katakana. Used in casual, playful contexts.
"I'm late, but is it okay?" "No problem!"
このくらいのミスなら問題ナッシングだよ。
A mistake like this is nothing to worry about.