Handle situation where only a root full_slug is passed.
Handle situation where only a root full_slug is passed.

i.e. "section/" would break the rsplit(). If there is no slug, we can safely raise a DoesNotExist.

texastribune/armstrong.core.tt_sections,texastribune/armstrong.core.tt_sections,texastribune/armstrong.core.tt_sections,armstrong/armstrong.core.arm_sections,armstrong/armstrong.core.arm_sections