Null is already an instance, no need to instantiate it anymore

Ignore-this: cfc4088786711e427c6f94579c5f4de6

darcs-hash:20100718083621-b22ec-8f031bfd148b99e77f4b65f230872ebd211eccce
Fixed falling back to the None device when opening an AudioMixer

Ignore-this: 26cc4f2e3841646e98f09919194b8e64

darcs-hash:20100719075934-1e3d8-ee7cebf641691bf57466668a8fc71c9bad5db518