Green’s Dictionary of Slang

(US black) everything is simple, there are no problems; usu. in answer to the question ‘How are you doing?’.

1972

D. Claerbaut Black Jargon in White America 57: ain’t nothin’ to it a curt, resisting reply often given to ‘What’s happening?’ or ‘How are You?’: What happenin’ man? Ain’t nothin to it.