nil no longer allowed in load-path?

[Ulrich Mueller]

While investigating why ECB wouldn't compile any more with recent
Emacs versions, I stumbled upon this:

   $ emacs -Q --batch --eval "(add-to-list 'load-path nil)"
   Wrong type argument: stringp, nil

This happens both with 24.4 and the trunk version, but not with 24.3.
The documentation for load-path seems to say that nil is legal as an
element.

Feature or bug?

Ulrich