GitLab

It turns out the use of nil in the :type of outline regexp was for
very hysterical raisons.  Prior to 2001-09-12T20:42:08Z!rms@gnu.org, the
default value was nil, then it was initialized afterwards.
Everywhere in the code assumes it cannot be nil, so no need to allow
that any more.

* lisp/outline.el (outline-regexp): No longer allow nil.
(outline-heading-end-regexp): Add safety predicate.