The following just appeared in the ChangeLog

> Fri Jan 11 06:13:14 2008  Nobuyoshi Nakada  <nobu / ruby-lang.org>
> 
>         * encoding.c (rb_to_encoding_index, rb_to_encoding): disallow nil.
>           [ruby-dev:33003]

This is an incompatible change to the original 1.9.0 release: it means 
that we can no longer use force_encoding(nil) as a way of saying "this 
string has no encoding--I want to see the unencoded bytes".    Instead 
we're forced to use something longer like force_encoding("binary") or 
force_encoding(Encoding::BINARY).

The ability to use nil as a synonym for ASCII-8BIT/BINARY allowed it to 
mean "no encoding".  I think that was a feature, and I urge to you make 
it work again.  (Not least because I documented the old behavior in my 
book, and that book is going to the printer.  It is too late for me to 
make any more changes to track API changes like this)

	David