There shouldn't be collisions. I mean that really: if you see a collision it's so much more likely that your computer / program / source of randomness is faulty [as in this case] than that the two random numbers collided that it's not worth considering the collision case.
But there can be collisions, at least in theory. And as we can see, in practice too.
Not checking for collisions because you trust that an RNG returns unique values is a fallacy and should be avoided. Especially since it's so easy to deal with the problem.
