  String propagation on a three-dimensional Lorentzian string orbifold with a
null singularity has been studied by Horowitz and Steif, and more recently by
Liu, Moore and Seiberg. We analyze the target space as a classical
gravitational background. The singularity becomes spacelike when an arbitrarily
small amount of matter is thrown at the singularity. This can be seen directly
by studying the null singularity as a limit of the M=0, J=0 BTZ black hole
metric.
