Use None as mountpoint for new snapshots
Use None as mountpoint for new snapshots

Default value for mountpoint is always None not an empty string.

AdamWill/blivet,rvykydal/blivet,jkonecny12/blivet,AdamWill/blivet,jkonecny12/blivet,vojtechtrefny/blivet,rvykydal/blivet,vojtechtrefny/blivet