code: function getkeys(req, res) {
    var keys = []
      // target command
      , tcmd = req.args[0]
      , def = Constants.MAP[tcmd];
    if(def) {
      keys = def.getKeys(req.args.slice(1));
    }
    res.send(null, keys);
  }
docs: Respond to the GETKEYS subcommand.
  
  Current version redis@2.8.19 does not actually appear to
  implement this: `command getkeys get key` results in an error.
  
  Therefore this implementation is a best guess as to the intended
  behaviour.
  
  This command cannot fail with an error so we just return an empty list
  for target commands that do not accept keys.
  
  Examples:
  
  command getkeys set key val         // ['key']
  command getkeys mset k1 v1 k2 v2    // ['k1', 'k2']
  command getkeys hset hash field val // ['hash']