Actually sending `nil` as the first param is what we want. Check out the `Dalli::Client` source: https://github.com/mperham/dalli/blob/master/lib/dalli/client.rb#L29

If it's nil, it will check for `ENV[MEMCACHE_SERVERS']` and then fallback to `localhost:11211`. We're just letting Dalli do most of the hard work instead of re-implementing those fallbacks here.