Tests: don't use None as a path stand-in
Tests: don't use None as a path stand-in

This triggered a crash in `syspath` on Windows.

lengtche/beets,Kraymer/beets,shamangeorge/beets,SusannaMaria/beets,madmouser1/beets,artemutin/beets,ibmibmibm/beets,mosesfistos1/beetbox,jackwilsdon/beets,beetbox/beets,lengtche/beets,xsteadfastx/beets,sampsyo/beets,xsteadfastx/beets,SusannaMaria/beets,madmouser1/beets,sampsyo/beets,beetbox/beets,SusannaMaria/beets,xsteadfastx/beets,Kraymer/beets,shamangeorge/beets,jackwilsdon/beets,mosesfistos1/beetbox,jcoady9/beets,artemutin/beets,lengtche/beets,MyTunesFreeMusic/privacy-policy,diego-plan9/beets,MyTunesFreeMusic/privacy-policy,beetbox/beets,artemutin/beets,shamangeorge/beets,ibmibmibm/beets,MyTunesFreeMusic/privacy-policy,SusannaMaria/beets,beetbox/beets,pkess/beets,ibmibmibm/beets,diego-plan9/beets,lengtche/beets,Kraymer/beets,Kraymer/beets,jcoady9/beets,sampsyo/beets,jackwilsdon/beets,jcoady9/beets,madmouser1/beets,jcoady9/beets,madmouser1/beets,mosesfistos1/beetbox,diego-plan9/beets,shamangeorge/beets,diego-plan9/beets,pkess/beets,MyTunesFreeMusic/privacy-policy,pkess/beets,ibmibmibm/beets,pkess/beets,mosesfistos1/beetbox,sampsyo/beets,artemutin/beets,xsteadfastx/beets,jackwilsdon/beets