NASA has not classified the planet Nibiru because, according to NASA scientists, it does not exist. It has never been detected by telescopes, and there is no evidence that it threatens or has threatened the Earth. Some people predicted that Nibiru would collide with the Earth in 2012.
Nibiru has not collided with Earth as of 2015. Moreover, if a planet-sized object was on a collision course with Earth, it would have perturbed the orbits of the planets and even knocked the moon out of its orbit, according to NASA. Evidence of Nibiru could be found even if the planet had invaded the solar system as long as 1 million years ago, but no evidence exists.