or None / not None

Hello,

I'm getting the following warning with 0.9.9:

brltty/Bindings/Python/brlapi.pyx:439:17: Warning: 'not None' will become t=
he default in a future version of Pyrex. Use 'or None' to allow passing Non=
e.

Adding "or None" indeed makes it disappear, but it's refused by older
versions.  How can I change my source to something that works both with
older and newer versions of pyrexc?

Samuel