Clarify the meaning of None in run_once
Clarify the meaning of None in run_once

mneumann/mio,dwrensha/mio,carllerche/mio,asomers/mio,murarth/mio,carllerche/mio,fuchsia-mirror/third_party-mio,mneumann/mio,asomers/mio,fuchsia-mirror/third_party-mio