In this CNBC interview from May. Start at 1:23 for the relevant question and answer, though he doesn't mention the conversion itself until 1:34.
I maintain: Calabria is far too smart and knowledgeable to mention the warrants and a conversion if those things were somehow illegal. The same goes for Moelis, and Bill Ackman, etc. A junior-to-common conversion is possible and that video proves it.