def DeregisterMountPoint(cls, mount_point):
    """Deregisters a path specification mount point.

    Args:
      mount_point (str): mount point identifier.

    Raises:
      KeyError: if the corresponding mount point is not set.
    """
    if mount_point not in cls._mount_points:
      raise KeyError('Mount point: {0:s} not set.'.format(mount_point))

    del cls._mount_points[mount_point]