See: https://travis-ci.org/hapijs/wreck/jobs/67856616

Basically, it is fine to shadow some variables like err in callback. If you didn't handle it at the top of the method you clearly don't care. I have never seen bugs because of err argument shadows. I am going to go over the warning in hapi and see which one I find useful and fix those. I'll be back here with my findings but just heads up that I am going to want to see this rule changed at least for some cases.