As long as you winterized your Ninja properly, why would it do any harm to ride it?
I put my bike away in early December and put in some SeaFoam in the gas tank to act as a stabilizer and fuel system cleaner and I connected my battery tender in January after going for a ride. Everything worked fine. It took a few tries to get it started, but after that it started right up.
Only bad thing was 34* F weather tends to be a little cold and waiting for the bike to warm up enough to actually drive it. But it was worth it!