In fact, in Puppet 2.7.x, scope.lookupvar returns ```"undefined"``` when getting an undefined variable whereas in Puppet 3.x it returns ```nil``` (and this module was developped for/with Puppet 2.7 originally).

If you want to change this test (which could be more simplified to ```if $blkid {```, you'll have to change line 49 too to get an empty string if ```scope.lookupvar``` returns ```"undefined"``` when using Puppet 2.7.x. (Hope I'm clear enough)