Twitch's ult versus Nexus

While I was playing Twitch earlier today, I decided to blow up the enemy nexus with spunk.... Sadly for me, my whole team was holding off the enemy, so I was alone when attacking the nexus (They kind of died, because they overstayed trying to take the nexus, but due to my stealth I was able to sneak over to the nexus). Now, to add in some spunk and flashiness to end the game, I activated my ult on Twitch and started attacking the nexus..... There's a problem, however... Every single last attack that I used on the nexus did zero damage.

TL/DR: Really.... I barely wrote anything. TL/DR(actual): Twitch + Twitch's Ultimate + Attacking enemy nexus = Zero damagez