bug#19324: 25.0.50; add-function and nil

[Stefan Monnier]

> Yes, I had expected this to work and obviously not so filed this bug.
> Otherwise it is not a bad workaround.

> Go to a buffer in text mode where the default
> eldoc-documentation-function is nil and eval

>   (add-function :around (local 'eldoc-documentation-function)
>                         (lambda (orig) (or (and orig (funcall orig)) 
> (ignore))))

> Move around to get the error.

Ah, right, damn: the (local <foo>) causes the insertion of a "proxy
function" which runs the global value, but that doesn't check if
it's nil.
IOW it only works for :override.


        Stefan