Indeed to get the free spins, it is not required to deposit but in order to wager the winning from the free spins, deposit is required.
Are you talking about Sherbet.com no-deposit free spins? You can complete the wagering requirement by playing with the free spin winnings, they aren't asking for deposits in that case. But you have to make a deposit of $20 at least in order to make the free spin winnings withdrawable. The deposit can be made after completing the 45× wager.
But still this promotion cannot be considered as a 'no deposit bonus'.