as best i can logic (my abilities here are extremely limited), i'd say only a public entity would ever consider lending at 0% or lower. they receive a payoff indirectly through generated activity and tax revenue so could stand the real upfront loss. no non-crooked private party would entertain lending with no interest (i certainly wouldn't).
If you had $800 million in cash, and you could either deposit it with the central bank and be paid -0.5% interest, or invest it in say, a 12-month Apple corporate bond at 0%, what would you do? Note that attempting to hold onto the cash in a vault has real costs as well.
