  It was believed that when gravitational, electromagnetic and scalar waves
interact, a spacelike curvature singularity or Cauchy horizon develops because
of mutual focusing. We show with an exact solution that the collision of
Einstein-Maxwell-Scalar fields, in contrast to previous studies, predicts
singularities on null surfaces and that this is a transition phase between
spacelike singularities and regular horizons. Divergences of tidal forces in
the null singularities is shown to be weaker relative to the spacelike ones.
Using the local isometry between colliding plane waves and black holes, we show
that the inner horizon of Reissner-Nordstrom black hole transforms into a null
singularity when a particular scalar field is coupled to it. We also present an
analytic exact solution, which represents a Reissner-Nordstrom black hole with
scalar hair in between the ergosphere.
