Reference for Makkot 30:1

מידי הוא טעמא אלא לרבי יוחנן האמר ליה רבי יוחנן לתנא תני בטלו חייב ולא בטלו פטור

Is [Rava and Ravin's] explanation coming to teach us anything but the reason of Rebbi Yochanon? Why Rebbi Yochanon is the one who told the teacher of baraisas to teach that he is liable for nullifying and exempt for not nullifying.

Jastrow